80 changed files with 1222 additions and 1174 deletions
--- a/.all-contributorsrc
+++ b/.all-contributorsrc
@ -820,97 +820,6 @@
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--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@ -1,48 +1,3 @@
 <a name="4.4.0"></a>
 ## 4.4.0 (2021-04-24)
 #### Bug Fixes
 *   Fix spelling error in main.rs ([91ee27f2](https://github.com/rust-lang/rustlings/commit/91ee27f22bd3797a9db57e5fd430801c170c5db8))
 *   typo in default out text ([644c49f1](https://github.com/rust-lang/rustlings/commit/644c49f1e04cbb24e95872b3a52b07d692ae3bc8))
 * **collections:**  Naming exercises for vectors and hashmap ([bef39b12](https://github.com/rust-lang/rustlings/commit/bef39b125961310b34b34871e480a82e82af4678))
 * **from_str:**
  *  Correct typos ([5f7c89f8](https://github.com/rust-lang/rustlings/commit/5f7c89f85db1f33da01911eaa479c3a2d4721678))
  *  test for error instead of unwrap/should_panic ([15e71535](https://github.com/rust-lang/rustlings/commit/15e71535f37cfaed36e22eb778728d186e2104ab))
  *   use trait objects for from_str ([c3e7b831](https://github.com/rust-lang/rustlings/commit/c3e7b831786c9172ed8bd5d150f3c432f242fba9))
 * **functions3:**  improve function argument type (#687) ([a6509cc4](https://github.com/rust-lang/rustlings/commit/a6509cc4d545d8825f01ddf7ee37823b372154dd))
 * **hashmap2:**  Update incorrect assertion (#660) ([72aaa15e](https://github.com/rust-lang/rustlings/commit/72aaa15e6ab4b72b3422f1c6356396e20a2a2bb8))
 * **info:**  Fix typo (#635) ([cddc1e86](https://github.com/rust-lang/rustlings/commit/cddc1e86e7ec744ee644cc774a4887b1a0ded3e8))
 * **iterators2:**  Moved errors out of tests. ([baf4ba17](https://github.com/rust-lang/rustlings/commit/baf4ba175ba6eb92989e3dd54ecbec4bedc9a863), closes [#359](https://github.com/rust-lang/rustlings/issues/359))
 * **iterators3:**  Enabled iterators3.rs to run without commented out tests. ([c6712dfc](https://github.com/rust-lang/rustlings/commit/c6712dfccd1a093e590ad22bbc4f49edc417dac0))
 * **main:**  Let find_exercise work with borrows ([347f30bd](https://github.com/rust-lang/rustlings/commit/347f30bd867343c5ace1097e085a1f7e356553f7))
 * **move_semantics4:**
  *  Remove redundant "instead" (#640) ([cc266d7d](https://github.com/rust-lang/rustlings/commit/cc266d7d80b91e79df3f61984f231b7f1587218e))
  *  Small readbility improvement (#617) ([10965920](https://github.com/rust-lang/rustlings/commit/10965920fbdf8a1efc85bed869e55a1787006404))
 * **option2:**  Rename uninformative variables (#675) ([b4de6594](https://github.com/rust-lang/rustlings/commit/b4de6594380636817d13c2677ec6f472a964cf43))
 * **quiz3:**  Force an answer to Q2 (#672) ([0d894e6f](https://github.com/rust-lang/rustlings/commit/0d894e6ff739943901e1ae8c904582e5c2f843bd))
 * **structs:**  Add 5.3 to structs/README (#652) ([6bd791f2](https://github.com/rust-lang/rustlings/commit/6bd791f2f44aa7f0ad926df767f6b1fa8f12a9a9))
 * **structs2:**  correct grammar in hint (#663) ([ebdb66c7](https://github.com/rust-lang/rustlings/commit/ebdb66c7bfb6d687a14cc511a559a222e6fc5de4))
 * **structs3:**
  * reword heading comment (#664) ([9f3e8c2d](https://github.com/rust-lang/rustlings/commit/9f3e8c2dde645e5264c2d2200e68842b5f47bfa3))
  *   add check to prevent naive implementation of is_international ([05a753fe](https://github.com/rust-lang/rustlings/commit/05a753fe6333d36dbee5f68c21dec04eacdc75df))
 * **threads1:**  line number correction ([7857b0a6](https://github.com/rust-lang/rustlings/commit/7857b0a689b0847f48d8c14cbd1865e3b812d5ca))
 * **try_from_into:**  use trait objects ([2e93a588](https://github.com/rust-lang/rustlings/commit/2e93a588e0abe8badb7eafafb9e7d073c2be5df8))
 #### Features
 *   Replace clap with argh ([7928122f](https://github.com/rust-lang/rustlings/commit/7928122fcef9ca7834d988b1ec8ca0687478beeb))
 *   Replace emojis when NO_EMOJI env variable present ([8d62a996](https://github.com/rust-lang/rustlings/commit/8d62a9963708dbecd9312e8bcc4b47049c72d155))
 *   Added iterators5.rs exercise. ([b29ea17e](https://github.com/rust-lang/rustlings/commit/b29ea17ea94d1862114af2cf5ced0e09c197dc35))
 * **arc1:**  Add more details to description and hint (#710) ([81be4044](https://github.com/rust-lang/rustlings/commit/81be40448777fa338ebced3b0bfc1b32d6370313))
 * **cli:**  Improve the list command with options, and then some ([8bbe4ff1](https://github.com/rust-lang/rustlings/commit/8bbe4ff1385c5c169c90cd3ff9253f9a91daaf8e))
 * **list:**
  *  updated progress percentage ([1c6f7e4b](https://github.com/rust-lang/rustlings/commit/1c6f7e4b7b9b3bd36f4da2bb2b69c549cc8bd913))
  *  added progress info ([c0e3daac](https://github.com/rust-lang/rustlings/commit/c0e3daacaf6850811df5bc57fa43e0f249d5cfa4))
 <a name="4.3.0"></a>
 ## 4.3.0 (2020-12-29)
--- a/Cargo.lock
+++ b/Cargo.lock
@ -2,42 +2,22 @@
 # It is not intended for manual editing.
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+ "winapi 0.3.8",
 "argh_shared",
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@ -52,49 +32,67 @@ dependencies = [
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 "libc",
- "winapi 0.3.9",
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 "winapi 0.3.8",
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 [[package]]
 name = "utf8-ranges"
 version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "796f7e48bef87609f7ade7e06495a87d5cd06c7866e6a5cbfceffc558a243737"
 [[package]]
 name = "vec_map"
 version = "0.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "05c78687fb1a80548ae3250346c3db86a80a7cdd77bda190189f2d0a0987c81a"
 [[package]]
 name = "walkdir"
-version = "2.3.2"
+version = "2.2.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "808cf2735cd4b6866113f648b791c6adc5714537bc222d9347bb203386ffda56"
+checksum = "9d9d7ed3431229a144296213105a390676cc49c9b6a72bd19f3176c98e129fa1"
 dependencies = [
 "same-file",
- "winapi 0.3.9",
+ "winapi 0.3.8",
 "winapi-util",
 ]
@ -699,9 +872,9 @@ checksum = "167dc9d6949a9b857f3451275e911c3f44255842c1f7a76f33c55103a909087a"
 [[package]]
 name = "winapi"
-version = "0.3.9"
+version = "0.3.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
+checksum = "8093091eeb260906a183e6ae1abdba2ef5ef2257a21801128899c3fc699229c6"
 dependencies = [
 "winapi-i686-pc-windows-gnu",
 "winapi-x86_64-pc-windows-gnu",
@ -721,11 +894,11 @@ checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
 [[package]]
 name = "winapi-util"
-version = "0.1.5"
+version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "70ec6ce85bb158151cae5e5c87f95a8e97d2c0c4b001223f33a334e3ce5de178"
+checksum = "7168bab6e1daee33b4557efd0e95d5ca70a03706d39fa5f3fe7a236f584b03c9"
 dependencies = [
- "winapi 0.3.9",
+ "winapi 0.3.8",
 ]
 [[package]]
--- a/Cargo.toml
+++ b/Cargo.toml
@ -1,11 +1,11 @@
 [package]
 name = "rustlings"
-version = "4.4.0"
+version = "4.3.0"
 authors = ["Marisa <mokou@posteo.de>", "Carol (Nichols || Goulding) <carol.nichols@gmail.com>"]
 edition = "2018"
 [dependencies]
-argh = "0.1.4"
+clap = "2.32.0"
 indicatif = "0.10.3"
 console = "0.7.7"
 notify = "4.0.15"
--- a/README.md
+++ b/README.md
@ -1,3 +1,285 @@
-# rustlings
+<!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
 [![All Contributors](https://img.shields.io/badge/all_contributors-88-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
-My solutions to rustlings excercises
+# rustlings 🦀❤️
 Greetings and welcome to `rustlings`. This project contains small exercises to get you used to reading and writing Rust code. This includes reading and responding to compiler messages!
 _...looking for the old, web-based version of Rustlings? Try [here](https://github.com/rust-lang/rustlings/tree/rustlings-1)_
 Alternatively, for a first-time Rust learner, there are several other resources:
 - [The Book](https://doc.rust-lang.org/book/index.html) - The most comprehensive resource for learning Rust, but a bit theoretical sometimes. You will be using this along with Rustlings!
 - [Rust By Example](https://doc.rust-lang.org/rust-by-example/index.html) - Learn Rust by solving little exercises! It's almost like `rustlings`, but online
 ## Getting Started
 _Note: If you're on MacOS, make sure you've installed Xcode and its developer tools by typing `xcode-select --install`._
 You will need to have Rust installed. You can get it by visiting https://rustup.rs. This'll also install Cargo, Rust's package/project manager.
 ## MacOS/Linux
 Just run:
 ```bash
 curl -L https://git.io/install-rustlings | bash
 # Or if you want it to be installed to a different path:
 curl -L https://git.io/install-rustlings | bash -s mypath/
 ```
 This will install Rustlings and give you access to the `rustlings` command. Run it to get started!
 ## Windows
 In PowerShell, set `ExecutionPolicy` to `RemoteSigned`:
 ```ps
 Set-ExecutionPolicy RemoteSigned
 ```
 Then, you can run:
 ```ps
 Start-BitsTransfer -Source https://git.io/JTL5v -Destination $env:TMP/install_rustlings.ps1; Unblock-File $env:TMP/install_rustlings.ps1; Invoke-Expression $env:TMP/install_rustlings.ps1
 ```
 To install Rustlings. Same as on MacOS/Linux, you will have access to the `rustlings` command after it.
 When you get a permission denied message then you have to exclude the directory where you placed the rustlings in your virus-scanner
 ## Browser:
 [Run on Repl.it](https://repl.it/github/rust-lang/rustlings)
 [Open in Gitpod](https://gitpod.io/#https://github.com/rust-lang/rustlings)
 ## Manually
 Basically: Clone the repository, checkout to the latest tag, run `cargo install`.
 ```bash
 git clone https://github.com/rust-lang/rustlings
 cd rustlings
 git checkout tags/4.3.0 # or whatever the latest version is (find out at https://github.com/rust-lang/rustlings/releases/latest)
 cargo install --force --path .
 ```
 If there are installation errors, ensure that your toolchain is up to date. For the latest, run:
 ```bash
 rustup update
 ```
 Then, same as above, run `rustlings` to get started.
 ## Doing exercises
 The exercises are sorted by topic and can be found in the subdirectory `rustlings/exercises/<topic>`. For every topic there is an additional README file with some resources to get you started on the topic. We really recommend that you have a look at them before you start.
 The task is simple. Most exercises contain an error that keeps them from compiling, and it's up to you to fix it! Some exercises are also run as tests, but rustlings handles them all the same. To run the exercises in the recommended order, execute:
 ```bash
 rustlings watch
 ```
 This will try to verify the completion of every exercise in a predetermined order (what we think is best for newcomers). It will also rerun automatically every time you change a file in the `exercises/` directory. If you want to only run it once, you can use:
 ```bash
 rustlings verify
 ```
 This will do the same as watch, but it'll quit after running.
 In case you want to go by your own order, or want to only verify a single exercise, you can run:
 ```bash
 rustlings run myExercise1
 ```
 In case you get stuck, you can run the following command to get a hint for your
 exercise:
 ``` bash
 rustlings hint myExercise1
 ```
 To check your progress, you can run the following command:
 ```bash
 rustlings list
 ```
 ## Testing yourself
 After every couple of sections, there will be a quiz that'll test your knowledge on a bunch of sections at once. These quizzes are found in `exercises/quizN.rs`.
 ## Continuing On
 Once you've completed Rustlings, put your new knowledge to good use! Continue practicing your Rust skills by building your own projects, contributing to Rustlings, or finding other open-source projects to contribute to.
 ## Uninstalling Rustlings
 If you want to remove Rustlings from your system, there's two steps. First, you'll need to remove the exercises folder that the install script created
 for you:
 ``` bash
 rm -rf rustlings # or your custom folder name, if you chose and or renamed it
 ```
 Second, since Rustlings got installed via `cargo install`, it's only reasonable to assume that you can also remove it using Cargo, and
 exactly that is the case. Run `cargo uninstall` to remove the `rustlings` binary:
 ``` bash
 cargo uninstall rustlings
 ```
 Now you should be done!
 ## Completion
 Rustlings isn't done; there are a couple of sections that are very experimental and don't have proper documentation. These include:
 - Errors (`exercises/errors/`)
 - Option (`exercises/option/`)
 - Result (`exercises/result/`)
 - Move Semantics (could still be improved, `exercises/move_semantics/`)
 Additionally, we could use exercises on a couple of topics:
 - Structs
 - Better ownership stuff
 - `impl`
 - ??? probably more
 If you are interested in improving or adding new ones, please feel free to contribute! Read on for more information :)
 ## Contributing
 See [CONTRIBUTING.md](./CONTRIBUTING.md).
 ## Contributors ✨
 Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/docs/en/emoji-key)):
 <!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section -->
 <!-- prettier-ignore-start -->
 <!-- markdownlint-disable -->
 <table>
  <tr>
    <td align="center"><a href="http://carol-nichols.com"><img src="https://avatars2.githubusercontent.com/u/193874?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Carol (Nichols &#124;&#124; Goulding)</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=carols10cents" title="Code">💻</a> <a href="#content-carols10cents" title="Content">🖋</a></td>
    <td align="center"><a href="https://twitter.com/QuietMisdreavus"><img src="https://avatars2.githubusercontent.com/u/5217170?v=4?s=100" width="100px;" alt=""/><br /><sub><b>QuietMisdreavus</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=QuietMisdreavus" title="Code">💻</a> <a href="#content-QuietMisdreavus" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/robertlugg"><img src="https://avatars0.githubusercontent.com/u/6054540?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Robert M Lugg</b></sub></a><br /><a href="#content-robertlugg" title="Content">🖋</a></td>
    <td align="center"><a href="https://hynek.me/about/"><img src="https://avatars3.githubusercontent.com/u/41240?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Hynek Schlawack</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=hynek" title="Code">💻</a></td>
    <td align="center"><a href="https://spacekookie.de"><img src="https://avatars0.githubusercontent.com/u/7669898?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Katharina Fey</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=spacekookie" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/lukabavdaz"><img src="https://avatars0.githubusercontent.com/u/9624558?v=4?s=100" width="100px;" alt=""/><br /><sub><b>lukabavdaz</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=lukabavdaz" title="Code">💻</a> <a href="#content-lukabavdaz" title="Content">🖋</a></td>
    <td align="center"><a href="http://vestera.as"><img src="https://avatars2.githubusercontent.com/u/4187449?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Erik Vesteraas</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=evestera" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/Delet0r"><img src="https://avatars1.githubusercontent.com/u/23195618?v=4?s=100" width="100px;" alt=""/><br /><sub><b>delet0r</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=Delet0r" title="Code">💻</a></td>
  </tr>
  <tr>
    <td align="center"><a href="http://phinary.ca"><img src="https://avatars1.githubusercontent.com/u/10522375?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Shaun Bennett</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=shaunbennett" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/abagshaw"><img src="https://avatars2.githubusercontent.com/u/8594541?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Andrew Bagshaw</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=abagshaw" title="Code">💻</a></td>
    <td align="center"><a href="https://ai6ua.net/"><img src="https://avatars2.githubusercontent.com/u/175578?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Kyle Isom</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=kisom" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/ColinPitrat"><img src="https://avatars3.githubusercontent.com/u/1541863?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Colin Pitrat</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=ColinPitrat" title="Code">💻</a></td>
    <td align="center"><a href="https://zacanger.com"><img src="https://avatars3.githubusercontent.com/u/12520493?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Zac Anger</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=zacanger" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/mgeier"><img src="https://avatars1.githubusercontent.com/u/705404?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Matthias Geier</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=mgeier" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/cjpearce"><img src="https://avatars1.githubusercontent.com/u/3453268?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Chris Pearce</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=cjpearce" title="Code">💻</a></td>
    <td align="center"><a href="https://yvan-sraka.github.io"><img src="https://avatars2.githubusercontent.com/u/705213?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Yvan Sraka</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=yvan-sraka" title="Code">💻</a></td>
  </tr>
  <tr>
    <td align="center"><a href="https://github.com/dendi239"><img src="https://avatars3.githubusercontent.com/u/16478650?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Denys Smirnov</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=dendi239" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/eddyp"><img src="https://avatars2.githubusercontent.com/u/123772?v=4?s=100" width="100px;" alt=""/><br /><sub><b>eddyp</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=eddyp" title="Code">💻</a></td>
    <td align="center"><a href="http://about.me/BrianKung"><img src="https://avatars1.githubusercontent.com/u/2836167?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Brian Kung</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=briankung" title="Code">💻</a> <a href="#content-briankung" title="Content">🖋</a></td>
    <td align="center"><a href="https://rcousineau.gitlab.io"><img src="https://avatars3.githubusercontent.com/u/281039?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Russell</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=miller-time" title="Code">💻</a></td>
    <td align="center"><a href="http://danwilhelm.com"><img src="https://avatars3.githubusercontent.com/u/6137185?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Dan Wilhelm</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=danwilhelm" title="Documentation">📖</a></td>
    <td align="center"><a href="https://github.com/Jesse-Cameron"><img src="https://avatars3.githubusercontent.com/u/3723654?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Jesse</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=Jesse-Cameron" title="Code">💻</a> <a href="#content-Jesse-Cameron" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/MrFroop"><img src="https://avatars3.githubusercontent.com/u/196700?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Fredrik Jambrén</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=MrFroop" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/petemcfarlane"><img src="https://avatars3.githubusercontent.com/u/3472717?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Pete McFarlane</b></sub></a><br /><a href="#content-petemcfarlane" title="Content">🖋</a></td>
  </tr>
  <tr>
    <td align="center"><a href="https://github.com/nkanderson"><img src="https://avatars0.githubusercontent.com/u/4128825?v=4?s=100" width="100px;" alt=""/><br /><sub><b>nkanderson</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=nkanderson" title="Code">💻</a> <a href="#content-nkanderson" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/ajaxm"><img src="https://avatars0.githubusercontent.com/u/13360138?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ajax M</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=ajaxm" title="Documentation">📖</a></td>
    <td align="center"><a href="https://dylnuge.com"><img src="https://avatars2.githubusercontent.com/u/118624?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Dylan Nugent</b></sub></a><br /><a href="#content-Dylnuge" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/vyaslav"><img src="https://avatars0.githubusercontent.com/u/1385427?v=4?s=100" width="100px;" alt=""/><br /><sub><b>vyaslav</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=vyaslav" title="Code">💻</a> <a href="#content-vyaslav" title="Content">🖋</a></td>
    <td align="center"><a href="https://join.sfxd.org"><img src="https://avatars1.githubusercontent.com/u/17297466?v=4?s=100" width="100px;" alt=""/><br /><sub><b>George</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=gdoenlen" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/nyxtom"><img src="https://avatars2.githubusercontent.com/u/222763?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Thomas Holloway</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=nyxtom" title="Code">💻</a> <a href="#content-nyxtom" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/workingjubilee"><img src="https://avatars1.githubusercontent.com/u/46493976?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Jubilee</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=workingjubilee" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/WofWca"><img src="https://avatars1.githubusercontent.com/u/39462442?v=4?s=100" width="100px;" alt=""/><br /><sub><b>WofWca</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=WofWca" title="Code">💻</a></td>
  </tr>
  <tr>
    <td align="center"><a href="https://github.com/jrvidal"><img src="https://avatars0.githubusercontent.com/u/1636604?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Roberto Vidal</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=jrvidal" title="Code">💻</a> <a href="https://github.com/rust-lang/rustlings/commits?author=jrvidal" title="Documentation">📖</a> <a href="#ideas-jrvidal" title="Ideas, Planning, & Feedback">🤔</a> <a href="#maintenance-jrvidal" title="Maintenance">🚧</a></td>
    <td align="center"><a href="https://github.com/jensim"><img src="https://avatars0.githubusercontent.com/u/3663856?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Jens</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=jensim" title="Documentation">📖</a></td>
    <td align="center"><a href="http://rahatah.me/d"><img src="https://avatars3.githubusercontent.com/u/3174006?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Rahat Ahmed</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=rahatarmanahmed" title="Documentation">📖</a></td>
    <td align="center"><a href="https://github.com/AbdouSeck"><img src="https://avatars2.githubusercontent.com/u/6490055?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Abdou Seck</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=AbdouSeck" title="Code">💻</a> <a href="#content-AbdouSeck" title="Content">🖋</a> <a href="https://github.com/rust-lang/rustlings/pulls?q=is%3Apr+reviewed-by%3AAbdouSeck" title="Reviewed Pull Requests">👀</a></td>
    <td align="center"><a href="https://codehearts.com"><img src="https://avatars0.githubusercontent.com/u/2885412?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Katie</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=codehearts" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/Socratides"><img src="https://avatars3.githubusercontent.com/u/27732983?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Socrates</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=Socratides" title="Documentation">📖</a></td>
    <td align="center"><a href="https://github.com/gnodarse"><img src="https://avatars3.githubusercontent.com/u/46761795?v=4?s=100" width="100px;" alt=""/><br /><sub><b>gnodarse</b></sub></a><br /><a href="#content-gnodarse" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/harrisonmetz"><img src="https://avatars1.githubusercontent.com/u/7883408?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Harrison Metzger</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=harrisonmetz" title="Code">💻</a></td>
  </tr>
  <tr>
    <td align="center"><a href="https://github.com/TorbenJ"><img src="https://avatars2.githubusercontent.com/u/9077102?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Torben Jonas</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=TorbenJ" title="Code">💻</a> <a href="#content-TorbenJ" title="Content">🖋</a></td>
    <td align="center"><a href="http://paulbissex.com/"><img src="https://avatars0.githubusercontent.com/u/641?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Paul Bissex</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=pbx" title="Documentation">📖</a></td>
    <td align="center"><a href="https://github.com/sjmann"><img src="https://avatars0.githubusercontent.com/u/6589896?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Steven Mann</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=sjmann" title="Code">💻</a> <a href="#content-sjmann" title="Content">🖋</a></td>
    <td align="center"><a href="https://smmdb.net/"><img src="https://avatars2.githubusercontent.com/u/5855071?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Mario Reder</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=Tarnadas" title="Code">💻</a> <a href="#content-Tarnadas" title="Content">🖋</a></td>
    <td align="center"><a href="https://keybase.io/skim"><img src="https://avatars0.githubusercontent.com/u/47347?v=4?s=100" width="100px;" alt=""/><br /><sub><b>skim</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=sl4m" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/sanjaykdragon"><img src="https://avatars1.githubusercontent.com/u/10261698?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Sanjay K</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=sanjaykdragon" title="Code">💻</a> <a href="#content-sanjaykdragon" title="Content">🖋</a></td>
    <td align="center"><a href="http://www.rohanjain.in"><img src="https://avatars1.githubusercontent.com/u/343499?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Rohan Jain</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=crodjer" title="Code">💻</a></td>
    <td align="center"><a href="https://www.saidaspen.se"><img src="https://avatars1.githubusercontent.com/u/7727687?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Said Aspen</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=saidaspen" title="Code">💻</a> <a href="#content-saidaspen" title="Content">🖋</a></td>
  </tr>
  <tr>
    <td align="center"><a href="https://github.com/uce"><img src="https://avatars3.githubusercontent.com/u/1756620?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ufuk Celebi</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=uce" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/lebedevsergey"><img src="https://avatars2.githubusercontent.com/u/7325764?v=4?s=100" width="100px;" alt=""/><br /><sub><b>lebedevsergey</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=lebedevsergey" title="Documentation">📖</a></td>
    <td align="center"><a href="https://github.com/avrong"><img src="https://avatars2.githubusercontent.com/u/6342851?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Aleksei Trifonov</b></sub></a><br /><a href="#content-avrong" title="Content">🖋</a></td>
    <td align="center"><a href="https://drn.ie"><img src="https://avatars2.githubusercontent.com/u/411136?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Darren Meehan</b></sub></a><br /><a href="#content-Darrenmeehan" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/jihchi"><img src="https://avatars1.githubusercontent.com/u/87983?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Jihchi Lee</b></sub></a><br /><a href="#content-jihchi" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/bertonha"><img src="https://avatars3.githubusercontent.com/u/1225902?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Christofer Bertonha</b></sub></a><br /><a href="#content-bertonha" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/apatniv"><img src="https://avatars2.githubusercontent.com/u/22565917?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Vivek Bharath Akupatni</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=apatniv" title="Code">💻</a> <a href="https://github.com/rust-lang/rustlings/commits?author=apatniv" title="Tests">⚠️</a></td>
    <td align="center"><a href="https://github.com/DiD92"><img src="https://avatars3.githubusercontent.com/u/6002416?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Dídac Sementé Fernández</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=DiD92" title="Code">💻</a> <a href="#content-DiD92" title="Content">🖋</a></td>
  </tr>
  <tr>
    <td align="center"><a href="https://github.com/wrobstory"><img src="https://avatars3.githubusercontent.com/u/2601457?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Rob Story</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=wrobstory" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/siobhanjacobson"><img src="https://avatars2.githubusercontent.com/u/28983835?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Siobhan Jacobson</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=siobhanjacobson" title="Code">💻</a></td>
    <td align="center"><a href="https://www.linkedin.com/in/evancarroll/"><img src="https://avatars2.githubusercontent.com/u/19922?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Evan Carroll</b></sub></a><br /><a href="#content-EvanCarroll" title="Content">🖋</a></td>
    <td align="center"><a href="http://www.jawaadmahmood.com"><img src="https://avatars3.githubusercontent.com/u/95606?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Jawaad Mahmood</b></sub></a><br /><a href="#content-jmahmood" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/GaurangTandon"><img src="https://avatars1.githubusercontent.com/u/6308683?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Gaurang Tandon</b></sub></a><br /><a href="#content-GaurangTandon" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/dev-cyprium"><img src="https://avatars1.githubusercontent.com/u/6002628?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Stefan Kupresak</b></sub></a><br /><a href="#content-dev-cyprium" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/greg-el"><img src="https://avatars3.githubusercontent.com/u/45019882?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Greg Leonard</b></sub></a><br /><a href="#content-greg-el" title="Content">🖋</a></td>
    <td align="center"><a href="https://ryanpcmcquen.org"><img src="https://avatars3.githubusercontent.com/u/772937?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ryan McQuen</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=ryanpcmcquen" title="Code">💻</a></td>
  </tr>
  <tr>
    <td align="center"><a href="https://github.com/AnnikaCodes"><img src="https://avatars3.githubusercontent.com/u/56906084?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Annika</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/pulls?q=is%3Apr+reviewed-by%3AAnnikaCodes" title="Reviewed Pull Requests">👀</a></td>
    <td align="center"><a href="https://darnuria.eu"><img src="https://avatars1.githubusercontent.com/u/2827553?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Axel Viala</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=darnuria" title="Code">💻</a></td>
    <td align="center"><a href="https://sazid.github.io"><img src="https://avatars1.githubusercontent.com/u/2370167?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Mohammed Sazid Al Rashid</b></sub></a><br /><a href="#content-sazid" title="Content">🖋</a> <a href="https://github.com/rust-lang/rustlings/commits?author=sazid" title="Code">💻</a></td>
    <td align="center"><a href="https://codingthemsoftly.com"><img src="https://avatars1.githubusercontent.com/u/17479099?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Caleb Webber</b></sub></a><br /><a href="#maintenance-seeplusplus" title="Maintenance">🚧</a></td>
    <td align="center"><a href="https://github.com/pcn"><img src="https://avatars2.githubusercontent.com/u/1056756?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Peter N</b></sub></a><br /><a href="#maintenance-pcn" title="Maintenance">🚧</a></td>
    <td align="center"><a href="https://github.com/seancad"><img src="https://avatars1.githubusercontent.com/u/47405611?v=4?s=100" width="100px;" alt=""/><br /><sub><b>seancad</b></sub></a><br /><a href="#maintenance-seancad" title="Maintenance">🚧</a></td>
    <td align="center"><a href="http://willhayworth.com"><img src="https://avatars3.githubusercontent.com/u/181174?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Will Hayworth</b></sub></a><br /><a href="#content-wsh" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/chrizel"><img src="https://avatars3.githubusercontent.com/u/20802?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Christian Zeller</b></sub></a><br /><a href="#content-chrizel" title="Content">🖋</a></td>
  </tr>
  <tr>
    <td align="center"><a href="https://github.com/jfchevrette"><img src="https://avatars.githubusercontent.com/u/3001?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Jean-Francois Chevrette</b></sub></a><br /><a href="#content-jfchevrette" title="Content">🖋</a> <a href="https://github.com/rust-lang/rustlings/commits?author=jfchevrette" title="Code">💻</a></td>
    <td align="center"><a href="https://github.com/jbaber"><img src="https://avatars.githubusercontent.com/u/1908117?v=4?s=100" width="100px;" alt=""/><br /><sub><b>John Baber-Lucero</b></sub></a><br /><a href="#content-jbaber" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/tal-zvon"><img src="https://avatars.githubusercontent.com/u/3195851?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Tal</b></sub></a><br /><a href="#content-tal-zvon" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/apogeeoak"><img src="https://avatars.githubusercontent.com/u/59737221?v=4?s=100" width="100px;" alt=""/><br /><sub><b>apogeeoak</b></sub></a><br /><a href="#content-apogeeoak" title="Content">🖋</a> <a href="https://github.com/rust-lang/rustlings/commits?author=apogeeoak" title="Code">💻</a></td>
    <td align="center"><a href="http://www.garfieldtech.com/"><img src="https://avatars.githubusercontent.com/u/254863?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Larry Garfield</b></sub></a><br /><a href="#content-Crell" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/circumspect"><img src="https://avatars.githubusercontent.com/u/40770208?v=4?s=100" width="100px;" alt=""/><br /><sub><b>circumspect</b></sub></a><br /><a href="#content-circumspect" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/cjwyett"><img src="https://avatars.githubusercontent.com/u/34195737?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Cyrus Wyett</b></sub></a><br /><a href="#content-cjwyett" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/cadolphs"><img src="https://avatars.githubusercontent.com/u/13894820?v=4?s=100" width="100px;" alt=""/><br /><sub><b>cadolphs</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=cadolphs" title="Code">💻</a></td>
  </tr>
  <tr>
    <td align="center"><a href="https://www.haveneer.com"><img src="https://avatars.githubusercontent.com/u/26146722?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Pascal H.</b></sub></a><br /><a href="#content-hpwxf" title="Content">🖋</a></td>
    <td align="center"><a href="https://twitter.com/chapeupreto"><img src="https://avatars.githubusercontent.com/u/834048?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Rod Elias</b></sub></a><br /><a href="#content-chapeupreto" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/blerchy"><img src="https://avatars.githubusercontent.com/u/2555355?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Matt Lebl</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=blerchy" title="Code">💻</a></td>
    <td align="center"><a href="http://flakolefluk.dev"><img src="https://avatars.githubusercontent.com/u/11986564?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ignacio Le Fluk</b></sub></a><br /><a href="#content-flakolefluk" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/tlyu"><img src="https://avatars.githubusercontent.com/u/431873?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Taylor Yu</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=tlyu" title="Code">💻</a> <a href="#content-tlyu" title="Content">🖋</a></td>
    <td align="center"><a href="https://zerotask.github.io"><img src="https://avatars.githubusercontent.com/u/20150243?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Patrick Hintermayer</b></sub></a><br /><a href="https://github.com/rust-lang/rustlings/commits?author=Zerotask" title="Code">💻</a></td>
    <td align="center"><a href="https://petkopavlovski.com/"><img src="https://avatars.githubusercontent.com/u/32264020?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Pete Pavlovski</b></sub></a><br /><a href="#content-arthas168" title="Content">🖋</a></td>
    <td align="center"><a href="https://github.com/k12ish"><img src="https://avatars.githubusercontent.com/u/45272873?v=4?s=100" width="100px;" alt=""/><br /><sub><b>k12ish</b></sub></a><br /><a href="#content-k12ish" title="Content">🖋</a></td>
  </tr>
 </table>
 <!-- markdownlint-restore -->
 <!-- prettier-ignore-end -->
 <!-- ALL-CONTRIBUTORS-LIST:END -->
 This project follows the [all-contributors](https://github.com/all-contributors/all-contributors) specification. Contributions of any kind welcome!
--- a/exercises/clippy/README.md
+++ b/exercises/clippy/README.md
@ -1,10 +1,8 @@
-# Clippy
+### Clippy
 The Clippy tool is a collection of lints to analyze your code so you can catch common mistakes and improve your Rust code.
 If you used the installation script for Rustlings, Clippy should be already installed.
 If not you can install it manually via `rustup component add clippy`.
-## Further information
+For more information about Clippy lints, please see [their documentation page](https://rust-lang.github.io/rust-clippy/master/).
 - [GitHub Repository](https://github.com/rust-lang/rust-clippy).
--- a/exercises/collections/README.md
+++ b/exercises/collections/README.md
@ -1,4 +1,4 @@
-# Collections
+### Collections
 Rust’s standard library includes a number of very useful data
 structures called collections. Most other data types represent one
@ -17,6 +17,4 @@ structures that are used very often in Rust programs:
  You may also know this by the names [*unordered map* in C++](https://en.cppreference.com/w/cpp/container/unordered_map), 
  [*dictionary* in Python](https://docs.python.org/3/tutorial/datastructures.html#dictionaries) or an *associative array* in other languages.
-## Further information
+[Rust book chapter](https://doc.rust-lang.org/stable/book/ch08-01-vectors.html)
 - [Storing Lists of Values with Vectors](https://doc.rust-lang.org/stable/book/ch08-01-vectors.html)
--- a/exercises/collections/hashmap1.rs
+++ b/exercises/collections/hashmap1.rs
@ -11,18 +11,18 @@
 // Execute the command `rustlings hint hashmap1` if you need
 // hints.
 // I AM NOT DONE
 use std::collections::HashMap;
 fn fruit_basket() -> HashMap<String, u32> {
-    let mut basket = HashMap::new(); // TODO: declare your hash map here.
+    let mut basket = // TODO: declare your hash map here.
    // Two bananas are already given for you :)
    basket.insert(String::from("banana"), 2);
    // TODO: Put more fruits in your basket here.
-    basket.insert(String::from("peach"), 2);
+
    basket.insert(String::from("mango"), 2);
    basket.insert(String::from("apple"), 2);
    basket
 }
--- a/exercises/collections/hashmap2.rs
+++ b/exercises/collections/hashmap2.rs
@ -12,6 +12,8 @@
 // Execute the command `rustlings hint hashmap2` if you need
 // hints.
 // I AM NOT DONE
 use std::collections::HashMap;
 #[derive(Hash, PartialEq, Eq)]
@ -33,9 +35,9 @@ fn fruit_basket(basket: &mut HashMap<Fruit, u32>) {
    ];
    for fruit in fruit_kinds {
-        if fruit == Fruit::Banana || fruit == Fruit::Pineapple {
+        // TODO: Put new fruits if not already present. Note that you
-            basket.insert(fruit, 4);
+        // are not allowed to put any type of fruit that's already
-        }
+        // present!
    }
 }
--- a/exercises/collections/vec1.rs
+++ b/exercises/collections/vec1.rs
@ -4,9 +4,11 @@
 // Make me compile and pass the test!
 // Execute the command `rustlings hint vec1` if you need hints.
 // I AM NOT DONE
 fn array_and_vec() -> ([i32; 4], Vec<i32>) {
    let a = [10, 20, 30, 40]; // a plain array
-    let v = vec![10,20,30,40]; // TODO: declare your vector here with the macro for vectors
+    let v = // TODO: declare your vector here with the macro for vectors
    (a, v)
 }
--- a/exercises/collections/vec2.rs
+++ b/exercises/collections/vec2.rs
@ -7,14 +7,12 @@
 // Execute the command `rustlings hint vec2` if you need
 // hints.
 // I AM NOT DONE
 fn vec_loop(mut v: Vec<i32>) -> Vec<i32> {
    for i in v.iter_mut() {
        // TODO: Fill this up so that each element in the Vec `v` is
        // multiplied by 2.
        // *i accesses a specific object in vector?
        // *= 2 multiplies it by 2
        *i *= 2;
    }
    // At this point, `v` should be equal to [4, 8, 12, 16, 20].
--- a/exercises/conversions/README.md
+++ b/exercises/conversions/README.md
@ -1,4 +1,5 @@
-# Type conversions
+### Type conversions
 Rust offers a multitude of ways to convert a value of a given type into another type.
@ -14,8 +15,6 @@ Furthermore, the `std::str` module offers a trait called [`FromStr`](https://doc
 These should be the main ways ***within the standard library*** to convert data into your desired types.
-## Further information
+#### Book Sections
-These are not directly covered in the book, but the standard library has a great documentation for it.
+These are not directly covered in the book, but the standard library has great documentation for [conversions here](https://doc.rust-lang.org/std/convert/index.html). The `FromStr` trait is also covered [here](https://doc.rust-lang.org/std/str/trait.FromStr.html).
 - [conversions](https://doc.rust-lang.org/std/convert/index.html)
 - [`FromStr` trait](https://doc.rust-lang.org/std/str/trait.FromStr.html)
--- a/exercises/enums/README.md
+++ b/exercises/enums/README.md
@ -1,10 +1,10 @@
-# Enums
+### Enums
 Rust allows you to define types called "enums" which enumerate possible values.
 Enums are a feature in many languages, but their capabilities differ in each language. Rust’s enums are most similar to algebraic data types in functional languages, such as F#, OCaml, and Haskell.
 Useful in combination with enums is Rust's "pattern matching" facility, which makes it easy to run different code for different values of an enumeration.
-## Further information
+#### Book Sections
 - [Enums](https://doc.rust-lang.org/book/ch06-00-enums.html)
 - [Pattern syntax](https://doc.rust-lang.org/book/ch18-03-pattern-syntax.html)
--- a/exercises/enums/enums1.rs
+++ b/exercises/enums/enums1.rs
@ -1,12 +1,11 @@
 // enums1.rs
 // Make me compile! Execute `rustlings hint enums1` for hints!
 // I AM NOT DONE
 #[derive(Debug)]
 enum Message {
-    Quit,
+    // TODO: define a few types of messages as used below
    Echo,
    Move,
    ChangeColor
 }
 fn main() {
--- a/exercises/enums/enums2.rs
+++ b/exercises/enums/enums2.rs
@ -1,12 +1,11 @@
 // enums2.rs
 // Make me compile! Execute `rustlings hint enums2` for hints!
 // I AM NOT DONE
 #[derive(Debug)]
 enum Message {
-    Move { x: i32, y: i32 },
+    // TODO: define the different variants used below
    Echo(String),
    ChangeColor(i32,i32,i32),
    Quit
 }
 impl Message {
--- a/exercises/enums/enums3.rs
+++ b/exercises/enums/enums3.rs
@ -1,11 +1,10 @@
 // enums3.rs
 // Address all the TODOs to make the tests pass!
 // I AM NOT DONE
 enum Message {
-    Move(Point),
+    // TODO: implement the message variant types based on their usage below
    Echo(String),
    ChangeColor((u8,u8,u8)),
    Quit
 }
 struct Point {
@ -38,13 +37,6 @@ impl State {
    fn process(&mut self, message: Message) {
        // TODO: create a match expression to process the different message variants
        match message {
            Message::ChangeColor((r,g,b)) => self.change_color((r,g,b)),
            Message::Echo(String) => self.echo(String),
            Message::Move(Pointer) => self.move_position(Pointer),
            Message::Quit => self.quit(),
            _ => panic!("NOTHING SUPPLIED D:"),
        }
    }
 }
--- a/exercises/error_handling/README.md
+++ b/exercises/error_handling/README.md
@ -1,11 +1,5 @@
-# Error handling
+For this exercise check out the sections:
 Most errors aren’t serious enough to require the program to stop entirely. 
 Sometimes, when a function fails, it’s for a reason that you can easily interpret and respond to.
 For example, if you try to open a file and that operation fails because the file doesn’t exist, you might want to create the file instead of terminating the process.
 ## Further information
 - [Error Handling](https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html)
 - [Generics](https://doc.rust-lang.org/book/ch10-01-syntax.html)
- [Result](https://doc.rust-lang.org/rust-by-example/error/result.html)
+
- [Boxing errors](https://doc.rust-lang.org/rust-by-example/error/multiple_error_types/boxing_errors.html)
+of the Rust Book.
--- a/exercises/error_handling/errors1.rs
+++ b/exercises/error_handling/errors1.rs
@ -6,12 +6,14 @@
 // this function to have.
 // Execute `rustlings hint errors1` for hints!
-pub fn generate_nametag_text(name: String) -> Result<String, String> {
+// I AM NOT DONE
 pub fn generate_nametag_text(name: String) -> Option<String> {
    if name.len() > 0 {
-        Ok(format!("Hi! My name is {}", name))
+        Some(format!("Hi! My name is {}", name))
    } else {
        // Empty names aren't allowed.
-        Err("Empty names aren't allowed.".to_owned())
+        None
    }
 }
@ -26,12 +28,11 @@ mod tests {
    fn generates_nametag_text_for_a_nonempty_name() {
        assert_eq!(
            generate_nametag_text("Beyoncé".into()),
-            Ok("Hi! My name is Beyoncé".into())
+            Some("Hi! My name is Beyoncé".into())
        );
    }
    #[test]
    #[should_panic]
    fn explains_why_generating_nametag_text_fails() {
        assert_eq!(
            generate_nametag_text("".into()),
--- a/exercises/error_handling/errors2.rs
+++ b/exercises/error_handling/errors2.rs
@ -16,12 +16,14 @@
 // There are at least two ways to implement this that are both correct-- but
 // one is a lot shorter! Execute `rustlings hint errors2` for hints to both ways.
 // I AM NOT DONE
 use std::num::ParseIntError;
 pub fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
    let processing_fee = 1;
    let cost_per_item = 5;
-    let qty = item_quantity.parse::<i32>()?;
+    let qty = item_quantity.parse::<i32>();
    Ok(qty * cost_per_item + processing_fee)
 }
--- a/exercises/error_handling/errors3.rs
+++ b/exercises/error_handling/errors3.rs
@ -4,12 +4,11 @@
 // Why not? What should we do to fix it?
 // Execute `rustlings hint errors3` for hints!
 // I AM NOT DONE
 use std::num::ParseIntError;
-// In previous excercises we were taught that Result can output
+fn main() {
 // i32 and ParseIntError, but nobody told us that Result can also
 // output () instead of i32... oops
 fn main() -> Result<(), ParseIntError> {
    let mut tokens = 100;
    let pretend_user_input = "8";
@ -21,8 +20,6 @@ fn main() -> Result<(), ParseIntError> {
        tokens -= cost;
        println!("You now have {} tokens.", tokens);
    }
    // No need for Err() because `?` operator already handles it well
    Ok(())
 }
 pub fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
--- a/exercises/error_handling/errorsn.rs
+++ b/exercises/error_handling/errorsn.rs
@ -17,17 +17,19 @@
 //
 // Execute `rustlings hint errorsn` for hints :)
 // I AM NOT DONE
 use std::error;
 use std::fmt;
 use std::io;
 // PositiveNonzeroInteger is a struct defined below the tests.
-fn read_and_validate(b: &mut dyn io::BufRead) -> Result<PositiveNonzeroInteger, Box<dyn error::Error>> {
+fn read_and_validate(b: &mut dyn io::BufRead) -> Result<PositiveNonzeroInteger, ???> {
    let mut line = String::new();
-    b.read_line(&mut line)?;
+    b.read_line(&mut line);
-    let num: i64 = line.trim().parse()?;
+    let num: i64 = line.trim().parse();
-    let answer = PositiveNonzeroInteger::new(num)?;
+    let answer = PositiveNonzeroInteger::new(num);
-    Ok(answer)
+    answer
 }
 //
--- a/exercises/functions/README.md
+++ b/exercises/functions/README.md
@ -1,7 +1,7 @@
-# Functions
+### Functions
 Here, you'll learn how to write functions and how Rust's compiler can trace things way back.
-## Further information
+#### Book Sections
 - [How Functions Work](https://doc.rust-lang.org/book/ch03-03-how-functions-work.html)
--- a/exercises/functions/functions1.rs
+++ b/exercises/functions/functions1.rs
@ -1,9 +1,8 @@
 // functions1.rs
 // Make me compile! Execute `rustlings hint functions1` for hints :)
 // I AM NOT DONE
 fn main() {
    call_me();
 }
 fn call_me() {
    println!("Called!");
 }
--- a/exercises/functions/functions2.rs
+++ b/exercises/functions/functions2.rs
@ -1,11 +1,13 @@
 // functions2.rs
 // Make me compile! Execute `rustlings hint functions2` for hints :)
 // I AM NOT DONE
 fn main() {
-    call_me(7);
+    call_me(3);
 }
-fn call_me(num:i32) {
+fn call_me(num:) {
    for i in 0..num {
        println!("Ring! Call number {}", i + 1);
    }
--- a/exercises/functions/functions3.rs
+++ b/exercises/functions/functions3.rs
@ -1,8 +1,10 @@
 // functions3.rs
 // Make me compile! Execute `rustlings hint functions3` for hints :)
 // I AM NOT DONE
 fn main() {
-    call_me(6);
+    call_me();
 }
 fn call_me(num: u32) {
--- a/exercises/functions/functions4.rs
+++ b/exercises/functions/functions4.rs
@ -4,12 +4,14 @@
 // This store is having a sale where if the price is an even number, you get
 // 10 Rustbucks off, but if it's an odd number, it's 3 Rustbucks off.
 // I AM NOT DONE
 fn main() {
    let original_price = 51;
    println!("Your sale price is {}", sale_price(original_price));
 }
-fn sale_price(price: i32) -> i32 {
+fn sale_price(price: i32) -> {
    if is_even(price) {
        price - 10
    } else {
--- a/exercises/functions/functions5.rs
+++ b/exercises/functions/functions5.rs
@ -1,17 +1,13 @@
 // functions5.rs
 // Make me compile! Execute `rustlings hint functions5` for hints :)
 // I AM NOT DONE
 fn main() {
    let answer = square(3);
    println!("The answer is {}", answer);
 }
 // without ; the expression is a return statement
 // it can be either both num * num or 
 // return num * num; 
 // but it cannot be
 // return num * num OR num * num;
 fn square(num: i32) -> i32 {
-    num * num
+    num * num;
 }
--- a/exercises/generics/README.md
+++ b/exercises/generics/README.md
@ -1,11 +1,7 @@
-# Generics
+### Generics
-Generics is the topic of generalizing types and functionalities to broader cases.
+In this section you'll learn about saving yourself many lines of code with generics!
 This is extremely useful for reducing code duplication in many ways, but can call for rather involving syntax.
 Namely, being generic requires taking great care to specify over which types a generic type is actually considered valid.
 The simplest and most common use of generics is for type parameters.
-## Further information
+### Book Sections
 - [Generic Data Types](https://doc.rust-lang.org/stable/book/ch10-01-syntax.html)
 - [Bounds](https://doc.rust-lang.org/rust-by-example/generics/bounds.html)
--- a/exercises/generics/generics1.rs
+++ b/exercises/generics/generics1.rs
@ -1,7 +1,9 @@
 // This shopping list program isn't compiling!
 // Use your knowledge of generics to fix it.
 // I AM NOT DONE
 fn main() {
-    let mut shopping_list: Vec<&str> = Vec::new();
+    let mut shopping_list: Vec<?> = Vec::new();
    shopping_list.push("milk");
 }
--- a/exercises/generics/generics2.rs
+++ b/exercises/generics/generics2.rs
@ -1,12 +1,14 @@
 // This powerful wrapper provides the ability to store a positive integer value.
 // Rewrite it using generics so that it supports wrapping ANY type.
-struct Wrapper<T> {
+// I AM NOT DONE
-    value: T,
+
 struct Wrapper {
    value: u32,
 }
-// <T> must be both for impl and Wrapper
+
-impl<T> Wrapper<T> {
+impl Wrapper {
-    pub fn new(value: T) -> Self {
+    pub fn new(value: u32) -> Self {
        Wrapper { value }
    }
 }
--- a/exercises/generics/generics3.rs
+++ b/exercises/generics/generics3.rs
@ -10,15 +10,15 @@
 // Execute 'rustlings hint generics3' for hints!
-pub struct ReportCard<T> {
+// I AM NOT DONE
-    pub grade: T,
+
 pub struct ReportCard {
    pub grade: f32,
    pub student_name: String,
    pub student_age: u8,
 }
-// <T> must implement std::fmt::Display or no format!() macro
+impl ReportCard {
 // for you
 impl<T: std::fmt::Display> ReportCard<T> {
    pub fn print(&self) -> String {
        format!("{} ({}) - achieved a grade of {}",
            &self.student_name, &self.student_age, &self.grade)
@ -46,7 +46,7 @@ mod tests {
    fn generate_alphabetic_report_card() {
        // TODO: Make sure to change the grade here after you finish the exercise.
        let report_card = ReportCard {
-            grade: "A+".to_string(),
+            grade: 2.1,
            student_name: "Gary Plotter".to_string(),
            student_age: 11,
        };
--- a/exercises/if/README.md
+++ b/exercises/if/README.md
@ -1,7 +1,7 @@
-# If
+### If
 `if`, the most basic type of control flow, is what you'll learn here.
-## Further information
+#### Book Sections
 - [Control Flow - if expressions](https://doc.rust-lang.org/book/ch03-05-control-flow.html#if-expressions)
--- a/exercises/if/if1.rs
+++ b/exercises/if/if1.rs
@ -1,16 +1,13 @@
 // if1.rs
 // I AM NOT DONE
 pub fn bigger(a: i32, b: i32) -> i32 {
    // Complete this function to return the bigger number!
    // Do not use:
    // - another function call
    // - additional variables
    // Execute `rustlings hint if1` for hints
 pub fn bigger(a: i32, b: i32) -> i32 {
    if a > b {
        a
    } else {
        b
    }
 }
 // Don't mind this for now :)
--- a/exercises/if/if2.rs
+++ b/exercises/if/if2.rs
@ -4,14 +4,13 @@
 // Step 2: Get the bar_for_fuzz and default_to_baz tests passing!
 // Execute the command `rustlings hint if2` if you want a hint :)
 // I AM NOT DONE
 pub fn fizz_if_foo(fizzish: &str) -> &str {
    if fizzish == "fizz" {
        "foo"
    } else if fizzish == "fuzz" {
        "bar"
    } else {
-        "baz"
+        1
    }
 }
--- a/exercises/macros/README.md
+++ b/exercises/macros/README.md
@ -1,10 +1,10 @@
-# Macros
+### Macros
 Rust's macro system is very powerful, but also kind of difficult to wrap your
 head around. We're not going to teach you how to write your own fully-featured
 macros. Instead, we'll show you how to use and create them.
-## Further information
+#### Book Sections
 - [Macros](https://doc.rust-lang.org/book/ch19-06-macros.html)
 - [The Little Book of Rust Macros](https://danielkeep.github.io/tlborm/book/index.html)
--- a/exercises/modules/README.md
+++ b/exercises/modules/README.md
@ -1,7 +1,7 @@
-# Modules
+### Modules
 In this section we'll give you an introduction to Rust's module system.
-## Further information
+#### Book Sections
 - [The Module System](https://doc.rust-lang.org/book/ch07-02-defining-modules-to-control-scope-and-privacy.html)
--- a/exercises/modules/modules1.rs
+++ b/exercises/modules/modules1.rs
@ -1,12 +1,10 @@
 // modules1.rs
 // Make me compile! Execute `rustlings hint modules1` for hints :)
-// `mod` defines a module which can contain functions, structs etc.
+// I AM NOT DONE
 // by default, its `fn`s only limited within itself, creating "closed
 // ecosystem". you can make them public with `pub`
 mod sausage_factory {
-    pub fn make_sausage() {
+    fn make_sausage() {
        println!("sausage!");
    }
 }
--- a/exercises/modules/modules2.rs
+++ b/exercises/modules/modules2.rs
@ -1,9 +1,11 @@
 // modules2.rs
 // Make me compile! Execute `rustlings hint modules2` for hints :)
 // I AM NOT DONE
 mod delicious_snacks {
-    pub use self::fruits::PEAR as fruit;
+    use self::fruits::PEAR as fruit;
-    pub use self::veggies::CUCUMBER as veggie;
+    use self::veggies::CUCUMBER as veggie;
    mod fruits {
        pub const PEAR: &'static str = "Pear";
--- a/exercises/move_semantics/README.md
+++ b/exercises/move_semantics/README.md
@ -1,8 +1,8 @@
-# Move Semantics
+### Move Semantics
 These exercises are adapted from [pnkfelix](https://github.com/pnkfelix)'s [Rust Tutorial](https://pnkfelix.github.io/rust-examples-icfp2014/) -- Thank you Felix!!!
-## Further information
+#### Book Sections
 For this section, the book links are especially important.
--- a/exercises/move_semantics/move_semantics1.rs
+++ b/exercises/move_semantics/move_semantics1.rs
@ -1,11 +1,12 @@
 // move_semantics1.rs
 // Make me compile! Execute `rustlings hint move_semantics1` for hints :)
 // I AM NOT DONE
 fn main() {
    let vec0 = Vec::new();
-    let mut vec1 = fill_vec(vec0);
+    let vec1 = fill_vec(vec0);
    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
--- a/exercises/move_semantics/move_semantics2.rs
+++ b/exercises/move_semantics/move_semantics2.rs
@ -2,10 +2,12 @@
 // Make me compile without changing line 13!
 // Execute `rustlings hint move_semantics2` for hints :)
 // I AM NOT DONE
 fn main() {
    let vec0 = Vec::new();
-    let mut vec1 = fill_vec(&vec0);
+    let mut vec1 = fill_vec(vec0);
    // Do not change the following line!
    println!("{} has length {} content `{:?}`", "vec0", vec0.len(), vec0);
@ -15,8 +17,8 @@ fn main() {
    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
 }
-fn fill_vec(vec: &[i32]) -> Vec<i32> {
+fn fill_vec(vec: Vec<i32>) -> Vec<i32> {
-    let mut vec = vec.to_vec();
+    let mut vec = vec;
    vec.push(22);
    vec.push(44);
--- a/exercises/move_semantics/move_semantics3.rs
+++ b/exercises/move_semantics/move_semantics3.rs
@ -3,10 +3,12 @@
 // (no lines with multiple semicolons necessary!)
 // Execute `rustlings hint move_semantics3` for hints :)
 // I AM NOT DONE
 fn main() {
    let vec0 = Vec::new();
-    let mut vec1 = fill_vec(&vec0);
+    let mut vec1 = fill_vec(vec0);
    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
@ -15,8 +17,7 @@ fn main() {
    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
 }
-fn fill_vec(vec: &[i32]) -> Vec<i32> { 
+fn fill_vec(vec: Vec<i32>) -> Vec<i32> {
    let mut vec = vec.to_vec();
    vec.push(22);
    vec.push(44);
    vec.push(66);
--- a/exercises/move_semantics/move_semantics4.rs
+++ b/exercises/move_semantics/move_semantics4.rs
@ -4,11 +4,12 @@
 // freshly created vector from fill_vec to its caller.
 // Execute `rustlings hint move_semantics4` for hints!
 // I AM NOT DONE
 fn main() {
-   // let vec0 = Vec::new();
+    let vec0 = Vec::new();
-    let mut vec1 = fill_vec();
+    let mut vec1 = fill_vec(vec0);
    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
@ -19,7 +20,7 @@ fn main() {
 // `fill_vec()` no longer takes `vec: Vec<i32>` as argument
 fn fill_vec() -> Vec<i32> {
-    let mut vec = Vec::new();
+    let mut vec = vec;
    vec.push(22);
    vec.push(44);
--- a/exercises/option/README.md
+++ b/exercises/option/README.md
@ -1,17 +1,8 @@
-# Option
+### Option
-Type Option represents an optional value: every Option is either Some and contains a value, or None, and does not. 
+#### Book Sections
 Option types are very common in Rust code, as they have a number of uses:
 - Initial values
 - Return values for functions that are not defined over their entire input range (partial functions)
 - Return value for otherwise reporting simple errors, where None is returned on error
 - Optional struct fields
 - Struct fields that can be loaned or "taken"
 - Optional function arguments
 - Nullable pointers
 - Swapping things out of difficult situations
-## Further Information
+To learn about Option<T>, check out these links:
 - [Option Enum Format](https://doc.rust-lang.org/stable/book/ch10-01-syntax.html#in-enum-definitions)
 - [Option Module Documentation](https://doc.rust-lang.org/std/option/)
--- a/exercises/option/option1.rs
+++ b/exercises/option/option1.rs
@ -9,16 +9,15 @@ fn print_number(maybe_number: Option<u16>) {
 }
 fn main() {
-    // rustc suggested solutions
+    print_number(13);
-    print_number(Some(13));
+    print_number(99);
    print_number(Some(99));
-    let numbers: [Option<u16>; 5];
+    let mut numbers: [Option<u16>; 5];
    for iter in 0..5 {
        let number_to_add: u16 = {
            ((iter * 1235) + 2) / (4 * 16)
        };
-        numbers[iter as usize] = Some(number_to_add);
+        numbers[iter as usize] = number_to_add;
    }
 }
--- a/exercises/primitive_types/README.md
+++ b/exercises/primitive_types/README.md
@ -1,9 +1,9 @@
-# Primitive Types
+### Primitive Types
 Rust has a couple of basic types that are directly implemented into the
 compiler. In this section, we'll go through the most important ones.
-## Further information
+#### Book Sections
 - [Data Types](https://doc.rust-lang.org/stable/book/ch03-02-data-types.html)
 - [The Slice Type](https://doc.rust-lang.org/stable/book/ch04-03-slices.html)
--- a/exercises/primitive_types/primitive_types1.rs
+++ b/exercises/primitive_types/primitive_types1.rs
@ -2,6 +2,8 @@
 // Fill in the rest of the line that has code missing!
 // No hints, there's no tricks, just get used to typing these :)
 // I AM NOT DONE
 fn main() {
    // Booleans (`bool`)
@ -10,7 +12,7 @@ fn main() {
        println!("Good morning!");
    }
-    let is_evening = true; // Finish the rest of this line like the example! Or make it be false!
+    let // Finish the rest of this line like the example! Or make it be false!
    if is_evening {
        println!("Good evening!");
    }
--- a/exercises/primitive_types/primitive_types2.rs
+++ b/exercises/primitive_types/primitive_types2.rs
@ -2,6 +2,8 @@
 // Fill in the rest of the line that has code missing!
 // No hints, there's no tricks, just get used to typing these :)
 // I AM NOT DONE
 fn main() {
    // Characters (`char`)
@ -14,7 +16,7 @@ fn main() {
        println!("Neither alphabetic nor numeric!");
    }
-    let your_character = 'D'; // Finish this line like the example! What's your favorite character?
+    let // Finish this line like the example! What's your favorite character?
    // Try a letter, try a number, try a special character, try a character
    // from a different language than your own, try an emoji!
    if your_character.is_alphabetic() {
--- a/exercises/primitive_types/primitive_types3.rs
+++ b/exercises/primitive_types/primitive_types3.rs
@ -2,9 +2,10 @@
 // Create an array with at least 100 elements in it where the ??? is.
 // Execute `rustlings hint primitive_types3` for hints!
 // I AM NOT DONE
 fn main() {
-    let a: [i32; 300] = [0; 300]; 
+    let a = ???
    if a.len() >= 100 {
        println!("Wow, that's a big array!");
--- a/exercises/primitive_types/primitive_types4.rs
+++ b/exercises/primitive_types/primitive_types4.rs
@ -2,11 +2,13 @@
 // Get a slice out of Array a where the ??? is so that the test passes.
 // Execute `rustlings hint primitive_types4` for hints!!
 // I AM NOT DONE
 #[test]
 fn slice_out_of_array() {
    let a = [1, 2, 3, 4, 5];
-    let nice_slice = &a[1..4];
+    let nice_slice = ???
    assert_eq!([2, 3, 4], nice_slice)
 }
--- a/exercises/primitive_types/primitive_types5.rs
+++ b/exercises/primitive_types/primitive_types5.rs
@ -2,9 +2,11 @@
 // Destructure the `cat` tuple so that the println will work.
 // Execute `rustlings hint primitive_types5` for hints!
 // I AM NOT DONE
 fn main() {
    let cat = ("Furry McFurson", 3.5);
-    let (name, age) = cat;
+    let /* your pattern here */ = cat;
    println!("{} is {} years old.", name, age);
 }
--- a/exercises/primitive_types/primitive_types6.rs
+++ b/exercises/primitive_types/primitive_types6.rs
@ -2,11 +2,14 @@
 // Use a tuple index to access the second element of `numbers`.
 // You can put the expression for the second element where ??? is so that the test passes.
 // Execute `rustlings hint primitive_types6` for hints!
 // I AM NOT DONE
 #[test]
 fn indexing_tuple() {
    let numbers = (1, 2, 3);
    // Replace below ??? with the tuple indexing syntax.
-    let second = numbers.1;
+    let second = ???;
    assert_eq!(2, second,
        "This is not the 2nd number in the tuple!")
--- a/exercises/quiz1.rs
+++ b/exercises/quiz1.rs
@ -7,16 +7,10 @@
 // more than 40 at once, each apple only costs 1! Write a function that calculates
 // the price of an order of apples given the order amount. No hints this time!
 // I AM NOT DONE
 // Put your function here!
 // fn ..... {
 fn calculate_apple_price(amount: i32) -> i32 {
    if amount > 40 {
        1 * amount
    } else {
        2 * amount
    }
 }
 // Don't modify this function!
 #[test]
--- a/exercises/quiz2.rs
+++ b/exercises/quiz2.rs
@ -7,6 +7,8 @@
 // you think each value is. That is, add either `string_slice` or `string`
 // before the parentheses on each line. If you're right, it will compile!
 // I AM NOT DONE
 fn string_slice(arg: &str) {
    println!("{}", arg);
 }
@ -15,14 +17,14 @@ fn string(arg: String) {
 }
 fn main() {
-    string_slice("blue");
+    ???("blue");
-    string("red".to_string());
+    ???("red".to_string());
-    string(String::from("hi"));
+    ???(String::from("hi"));
-    string("rust is fun!".to_owned());
+    ???("rust is fun!".to_owned());
-    string("nice weather".into());
+    ???("nice weather".into());
-    string(format!("Interpolation {}", "Station"));
+    ???(format!("Interpolation {}", "Station"));
-    string_slice(&String::from("abc")[0..1]);
+    ???(&String::from("abc")[0..1]);
-    string_slice("  hello there ".trim());
+    ???("  hello there ".trim());
-    string("Happy Monday!".to_string().replace("Mon", "Tues"));
+    ???("Happy Monday!".to_string().replace("Mon", "Tues"));
-    string("mY sHiFt KeY iS sTiCkY".to_lowercase());
+    ???("mY sHiFt KeY iS sTiCkY".to_lowercase());
 }
--- a/exercises/standard_library_types/README.md
+++ b/exercises/standard_library_types/README.md
@ -1,10 +1,5 @@
-# Standard library types
+For the Box exercise check out the chapter [Using Box to Point to Data on the Heap](https://doc.rust-lang.org/book/ch15-01-box.html).
-This section will teach you about Box, Shared-State Concurrency and Iterators.
+For the Arc exercise check out the chapter [Shared-State Concurrency](https://doc.rust-lang.org/book/ch16-03-shared-state.html) of the Rust Book.
-## Further information
+For the Iterator exercise check out the chapters [Iterator](https://doc.rust-lang.org/book/ch13-02-iterators.html) of the Rust Book and the [Iterator documentation](https://doc.rust-lang.org/stable/std/iter/).
 - [Using Box to Point to Data on the Heap](https://doc.rust-lang.org/book/ch15-01-box.html)
 - [Shared-State Concurrency](https://doc.rust-lang.org/book/ch16-03-shared-state.html)
 - [Iterator](https://doc.rust-lang.org/book/ch13-02-iterators.html)
 - [Iterator documentation](https://doc.rust-lang.org/stable/std/iter/)
--- a/exercises/standard_library_types/arc1.rs
+++ b/exercises/standard_library_types/arc1.rs
@ -1,21 +1,7 @@
 // arc1.rs
 // In this exercise, we are given a Vec of u32 called "numbers" with values ranging
 // from 0 to 99 -- [ 0, 1, 2, ..., 98, 99 ]
 // We would like to use this set of numbers within 8 different threads simultaneously.
 // Each thread is going to get the sum of every eighth value, with an offset.
 // The first thread (offset 0), will sum 0, 8, 16, ...
 // The second thread (offset 1), will sum 1, 9, 17, ...
 // The third thread (offset 2), will sum 2, 10, 18, ...
 // ...
 // The eighth thread (offset 7), will sum 7, 15, 23, ...
 // Because we are using threads, our values need to be thread-safe.  Therefore,
 // we are using Arc.  We need to make a change in each of the two TODOs.
 // Make this code compile by filling in a value for `shared_numbers` where the
-// first TODO comment is, and create an initial binding for `child_numbers`
+// TODO comment is and create an initial binding for `child_numbers`
-// where the second TODO comment is. Try not to create any copies of the `numbers` Vec!
+// somewhere. Try not to create any copies of the `numbers` Vec!
 // Execute `rustlings hint arc1` for hints :)
 // I AM NOT DONE
@ -30,7 +16,6 @@ fn main() {
    let mut joinhandles = Vec::new();
    for offset in 0..8 {
        let child_numbers = // TODO
        joinhandles.push(thread::spawn(move || {
            let mut i = offset;
            let mut sum = 0;
--- a/exercises/standard_library_types/iterators2.rs
+++ b/exercises/standard_library_types/iterators2.rs
@ -1,41 +1,28 @@
 // iterators2.rs
-// In this exercise, you'll learn some of the unique advantages that iterators
+// In this module, you'll learn some of the unique advantages that iterators can offer.
-// can offer. Follow the steps to complete the exercise.
+// Step 1. Complete the `capitalize_first` function to pass the first two cases.
 // Step 2. Apply the `capitalize_first` function to a vector of strings.
 //         Ensure that it returns a vector of strings as well.
 // Step 3. Apply the `capitalize_first` function again to a list.
 //         Try to ensure it returns a single string.
 // As always, there are hints if you execute `rustlings hint iterators2`!
 // I AM NOT DONE
 // Step 1.
 // Complete the `capitalize_first` function.
 // "hello" -> "Hello"
 pub fn capitalize_first(input: &str) -> String {
    let mut c = input.chars();
    match c.next() {
        None => String::new(),
-        Some(first) => ???,
+        Some(first) => first.collect::<String>() + c.as_str(),
    }
 }
 // Step 2.
 // Apply the `capitalize_first` function to a slice of string slices.
 // Return a vector of strings.
 // ["hello", "world"] -> ["Hello", "World"]
 pub fn capitalize_words_vector(words: &[&str]) -> Vec<String> {
    vec![]
 }
 // Step 3.
 // Apply the `capitalize_first` function again to a slice of string slices.
 // Return a single string.
 // ["hello", " ", "world"] -> "Hello World"
 pub fn capitalize_words_string(words: &[&str]) -> String {
    String::new()
 }
 #[cfg(test)]
 mod tests {
    use super::*;
    // Step 1.
    // Tests that verify your `capitalize_first` function implementation
    #[test]
    fn test_success() {
        assert_eq!(capitalize_first("hello"), "Hello");
@ -46,15 +33,18 @@ mod tests {
        assert_eq!(capitalize_first(""), "");
    }
    // Step 2.
    #[test]
    fn test_iterate_string_vec() {
        let words = vec!["hello", "world"];
-        assert_eq!(capitalize_words_vector(&words), ["Hello", "World"]);
+        let capitalized_words: Vec<String> = // TODO
        assert_eq!(capitalized_words, ["Hello", "World"]);
    }
    #[test]
    fn test_iterate_into_string() {
        let words = vec!["hello", " ", "world"];
-        assert_eq!(capitalize_words_string(&words), "Hello World");
+        let capitalized_words = // TODO
        assert_eq!(capitalized_words, "Hello World");
    }
 }
--- a/exercises/standard_library_types/iterators3.rs
+++ b/exercises/standard_library_types/iterators3.rs
@ -1,10 +1,11 @@
 // iterators3.rs
 // This is a bigger exercise than most of the others! You can do it!
 // Here is your mission, should you choose to accept it:
-// 1. Complete the divide function to get the first four tests to pass.
+// 1. Complete the divide function to get the first four tests to pass
-// 2. Get the remaining tests to pass by completing the result_with_list and
+// 2. Uncomment the last two tests and get them to pass by filling in
-//    list_of_results functions.
+//    values for `x` using `division_results`.
 // Execute `rustlings hint iterators3` to get some hints!
 // Have fun :-)
 // I AM NOT DONE
@ -20,28 +21,16 @@ pub struct NotDivisibleError {
    divisor: i32,
 }
-// Calculate `a` divided by `b` if `a` is evenly divisible by `b`.
+// This function should calculate `a` divided by `b` if `a` is
-// Otherwise, return a suitable error.
+// evenly divisible by b.
 // Otherwise, it should return a suitable error.
 pub fn divide(a: i32, b: i32) -> Result<i32, DivisionError> {}
 // Complete the function and return a value of the correct type so the test passes.
 // Desired output: Ok([1, 11, 1426, 3])
 fn result_with_list() -> () {
    let numbers = vec![27, 297, 38502, 81];
    let division_results = numbers.into_iter().map(|n| divide(n, 27));
 }
 // Complete the function and return a value of the correct type so the test passes.
 // Desired output: [Ok(1), Ok(11), Ok(1426), Ok(3)]
 fn list_of_results() -> () {
    let numbers = vec![27, 297, 38502, 81];
    let division_results = numbers.into_iter().map(|n| divide(n, 27));
 }
 #[cfg(test)]
 mod tests {
    use super::*;
    // Tests that verify your `divide` function implementation
    #[test]
    fn test_success() {
        assert_eq!(divide(81, 9), Ok(9));
@ -68,16 +57,22 @@ mod tests {
        assert_eq!(divide(0, 81), Ok(0));
    }
    // Iterator exercises using your `divide` function
    /*
    #[test]
-    fn test_result_with_list() {
+    fn result_with_list() {
-        assert_eq!(format!("{:?}", result_with_list()), "Ok([1, 11, 1426, 3])");
+        let numbers = vec![27, 297, 38502, 81];
        let division_results = numbers.into_iter().map(|n| divide(n, 27));
        let x //... Fill in here!
        assert_eq!(format!("{:?}", x), "Ok([1, 11, 1426, 3])");
    }
    #[test]
-    fn test_list_of_results() {
+    fn list_of_results() {
-        assert_eq!(
+        let numbers = vec![27, 297, 38502, 81];
-            format!("{:?}", list_of_results()),
+        let division_results = numbers.into_iter().map(|n| divide(n, 27));
-            "[Ok(1), Ok(11), Ok(1426), Ok(3)]"
+        let x //... Fill in here!
-        );
+        assert_eq!(format!("{:?}", x), "[Ok(1), Ok(11), Ok(1426), Ok(3)]");
    }
    */
 }
--- a/exercises/standard_library_types/iterators5.rs
+++ b/exercises/standard_library_types/iterators5.rs
@ -1,124 +0,0 @@
 // iterators5.rs
 // Let's define a simple model to track Rustlings exercise progress. Progress
 // will be modelled using a hash map. The name of the exercise is the key and
 // the progress is the value. Two counting functions were created to count the
 // number of exercises with a given progress. These counting functions use
 // imperative style for loops. Recreate this counting functionality using
 // iterators. Only the two iterator methods (count_iterator and
 // count_collection_iterator) need to be modified.
 // Execute `rustlings hint
 // iterators5` for hints.
 //
 // Make the code compile and the tests pass.
 // I AM NOT DONE
 use std::collections::HashMap;
 #[derive(PartialEq, Eq)]
 enum Progress {
    None,
    Some,
    Complete,
 }
 fn count_for(map: &HashMap<String, Progress>, value: Progress) -> usize {
    let mut count = 0;
    for val in map.values() {
        if val == &value {
            count += 1;
        }
    }
    count
 }
 fn count_iterator(map: &HashMap<String, Progress>, value: Progress) -> usize {
    // map is a hashmap with String keys and Progress values.
    // map = { "variables1": Complete, "from_str": None, ... }
 }
 fn count_collection_for(collection: &[HashMap<String, Progress>], value: Progress) -> usize {
    let mut count = 0;
    for map in collection {
        for val in map.values() {
            if val == &value {
                count += 1;
            }
        }
    }
    count
 }
 fn count_collection_iterator(collection: &[HashMap<String, Progress>], value: Progress) -> usize {
    // collection is a slice of hashmaps.
    // collection = [{ "variables1": Complete, "from_str": None, ... },
    //     { "variables2": Complete, ... }, ... ]
 }
 #[cfg(test)]
 mod tests {
    use super::*;
    #[test]
    fn count_complete() {
        let map = get_map();
        assert_eq!(3, count_iterator(&map, Progress::Complete));
    }
    #[test]
    fn count_equals_for() {
        let map = get_map();
        assert_eq!(
            count_for(&map, Progress::Complete),
            count_iterator(&map, Progress::Complete)
        );
    }
    #[test]
    fn count_collection_complete() {
        let collection = get_vec_map();
        assert_eq!(
            6,
            count_collection_iterator(&collection, Progress::Complete)
        );
    }
    #[test]
    fn count_collection_equals_for() {
        let collection = get_vec_map();
        assert_eq!(
            count_collection_for(&collection, Progress::Complete),
            count_collection_iterator(&collection, Progress::Complete)
        );
    }
    fn get_map() -> HashMap<String, Progress> {
        use Progress::*;
        let mut map = HashMap::new();
        map.insert(String::from("variables1"), Complete);
        map.insert(String::from("functions1"), Complete);
        map.insert(String::from("hashmap1"), Complete);
        map.insert(String::from("arc1"), Some);
        map.insert(String::from("as_ref_mut"), None);
        map.insert(String::from("from_str"), None);
        map
    }
    fn get_vec_map() -> Vec<HashMap<String, Progress>> {
        use Progress::*;
        let map = get_map();
        let mut other = HashMap::new();
        other.insert(String::from("variables2"), Complete);
        other.insert(String::from("functions2"), Complete);
        other.insert(String::from("if1"), Complete);
        other.insert(String::from("from_into"), None);
        other.insert(String::from("try_from_into"), None);
        vec![map, other]
    }
 }
--- a/exercises/strings/README.md
+++ b/exercises/strings/README.md
@ -1,9 +1,9 @@
-# Strings
+### Strings
 Rust has two string types, a string slice (`&str`) and an owned string (`String`).
 We're not going to dictate when you should use which one, but we'll show you how
 to identify and create them, as well as use them.
-## Further information
+#### Book Sections
 - [Strings](https://doc.rust-lang.org/book/ch08-02-strings.html)
--- a/exercises/strings/strings1.rs
+++ b/exercises/strings/strings1.rs
@ -2,13 +2,13 @@
 // Make me compile without changing the function signature!
 // Execute `rustlings hint strings1` for hints ;)
 // I AM NOT DONE
 fn main() {
    let answer = current_favorite_color();
    println!("My current favorite color is {}", answer);
 }
 fn current_favorite_color() -> String {
-    // .to_string uses fmt trait
+    "blue"
    // .to_owned works too
    "blue".to_owned()
 }
--- a/exercises/strings/strings2.rs
+++ b/exercises/strings/strings2.rs
@ -2,6 +2,8 @@
 // Make me compile without changing the function signature!
 // Execute `rustlings hint strings2` for hints :)
 // I AM NOT DONE
 fn main() {
    let word = String::from("green"); // Try not changing this line :)
    if is_a_color_word(word) {
@ -11,6 +13,6 @@ fn main() {
    }
 }
-fn is_a_color_word(attempt: String) -> bool {
+fn is_a_color_word(attempt: &str) -> bool {
    attempt == "green" || attempt == "blue" || attempt == "red"
 }
--- a/exercises/structs/README.md
+++ b/exercises/structs/README.md
@ -1,8 +1,7 @@
-# Structs
+### Structs
 Rust has three struct types: a classic C struct, a tuple struct, and a unit struct.
-## Further information
+#### Book Sections
 - [Structures](https://doc.rust-lang.org/book/ch05-01-defining-structs.html)
 - [Method Syntax](https://doc.rust-lang.org/book/ch05-03-method-syntax.html)
--- a/exercises/structs/structs1.rs
+++ b/exercises/structs/structs1.rs
@ -1,12 +1,13 @@
 // structs1.rs
 // Address all the TODOs to make the tests pass!
 // I AM NOT DONE
 struct ColorClassicStruct {
-    name: String,
+    // TODO: Something goes here
    hex: String
 }
-struct ColorTupleStruct(String, String);
+struct ColorTupleStruct(/* TODO: Something goes here */);
 #[derive(Debug)]
 struct UnitStruct;
@ -18,10 +19,8 @@ mod tests {
    #[test]
    fn classic_c_structs() {
        // TODO: Instantiate a classic c struct!
-        let green = ColorClassicStruct { 
+        // let green =
-            name: String::from("green"), 
+
            hex: String::from("#00FF00")
        };
        assert_eq!(green.name, "green");
        assert_eq!(green.hex, "#00FF00");
    }
@ -29,7 +28,7 @@ mod tests {
    #[test]
    fn tuple_structs() {
        // TODO: Instantiate a tuple struct!
-        let green = ColorTupleStruct("green".to_string(),"#00FF00".to_string());
+        // let green =
        assert_eq!(green.0, "green");
        assert_eq!(green.1, "#00FF00");
@ -38,7 +37,7 @@ mod tests {
    #[test]
    fn unit_structs() {
        // TODO: Instantiate a unit struct!
-        let unit_struct = UnitStruct;
+        // let unit_struct =
        let message = format!("{:?}s are fun!", unit_struct);
        assert_eq!(message, "UnitStructs are fun!");
--- a/exercises/structs/structs2.rs
+++ b/exercises/structs/structs2.rs
@ -1,6 +1,8 @@
 // structs2.rs
 // Address all the TODOs to make the tests pass!
 // I AM NOT DONE
 #[derive(Debug)]
 struct Order {
    name: String,
@ -32,15 +34,7 @@ mod tests {
    fn your_order() {
        let order_template = create_order_template();
        // TODO: Create your own order using the update syntax and template above!
-        let your_order = Order {
+        // let your_order =
            name: String::from("Hacker in Rust"),
            year: 2019,
            made_by_phone: false,
            made_by_mobile: false,
            made_by_email: true,
            item_number: 123,
            count: 1,
        };
        assert_eq!(your_order.name, "Hacker in Rust");
        assert_eq!(your_order.year, order_template.year);
        assert_eq!(your_order.made_by_phone, order_template.made_by_phone);
--- a/exercises/structs/structs3.rs
+++ b/exercises/structs/structs3.rs
@ -4,6 +4,7 @@
 // Make the code compile and the tests pass!
 // If you have issues execute `rustlings hint structs3`
 // I AM NOT DONE
 #[derive(Debug)]
 struct Package {
@ -15,7 +16,7 @@ struct Package {
 impl Package {
    fn new(sender_country: String, recipient_country: String, weight_in_grams: i32) -> Package {
        if weight_in_grams <= 0 {
-            panic!("Weight is in negative value.");
+            // Something goes here...
        } else {
            return Package {
                sender_country,
@ -25,20 +26,12 @@ impl Package {
        }
    }
-    fn is_international(&self) -> bool {
+    fn is_international(&self) -> ??? {
-        if self.sender_country != self.recipient_country {
+        // Something goes here...
            true
        } else {
            false
        }
    }
-    fn get_fees(&self, cents_per_gram: i32) -> i32 {
+    fn get_fees(&self, cents_per_gram: i32) -> ??? {
-        if cents_per_gram <= 0 {
+        // Something goes here... 
            panic!("We don't pay people, do we?");
        } else {
            cents_per_gram * self.weight_in_grams
        }
    }
 }
@ -80,7 +73,7 @@ mod tests {
        let sender_country = String::from("Spain");
        let recipient_country = String::from("Spain");
-        let cents_per_gram = 3;
+        let cents_per_gram = ???;
        let package = Package::new(sender_country, recipient_country, 1500);
--- a/exercises/tests/README.md
+++ b/exercises/tests/README.md
@ -1,7 +1,7 @@
-# Tests
+### Tests
 Going out of order from the book to cover tests -- many of the following exercises will ask you to make tests pass!
-## Further information
+#### Book Sections
 - [Writing Tests](https://doc.rust-lang.org/book/ch11-01-writing-tests.html)
--- a/exercises/threads/README.md
+++ b/exercises/threads/README.md
@ -1,9 +1 @@
-# Threads
+For this exercise check out the [Dining Philosophers example](https://doc.rust-lang.org/1.4.0/book/dining-philosophers.html) and the chapter [Concurrency](https://doc.rust-lang.org/book/ch16-01-threads.html) of the Rust Book.
 In most current operating systems, an executed program’s code is run in a process, and the operating system manages multiple processes at once.
 Within your program, you can also have independent parts that run simultaneously. The features that run these independent parts are called threads.
 ## Further information
 - [Dining Philosophers example](https://doc.rust-lang.org/1.4.0/book/dining-philosophers.html)
 - [Using Threads to Run Code Simultaneously](https://doc.rust-lang.org/book/ch16-01-threads.html)
--- a/exercises/traits/README.md
+++ b/exercises/traits/README.md
@ -1,4 +1,4 @@
-# Traits
+### Traits
 A trait is a collection of methods.
@ -7,13 +7,14 @@ Data types can implement traits. To do so, the methods making up the trait are d
 In this way, traits are somewhat similar to Java interfaces and C++ abstract classes.
 Some additional common Rust traits include:
- `Clone` (the `clone` method)
+
- `Display` (which allows formatted display via `{}`)
+ `Clone` (the `clone` method),
- `Debug` (which allows formatted display via `{:?}`)
+ `Display` (which allows formatted display via `{}`), and
 + `Debug` (which allows formatted display via `{:?}`).
 Because traits indicate shared behavior between data types, they are useful when writing generics.
-## Further information
+#### Book Sections
 - [Traits](https://doc.rust-lang.org/book/ch10-02-traits.html)
--- a/exercises/variables/README.md
+++ b/exercises/variables/README.md
@ -1,9 +1,7 @@
-# Variables
+### Variables
-In Rust, variables are immutable by default.
+Here you'll learn about simple variables.
 When a variable is immutable, once a value is bound to a name, you can’t change that value.
 You can make them mutable by adding mut in front of the variable name.
-## Further information
+#### Book Sections
 - [Variables and Mutability](https://doc.rust-lang.org/book/ch03-01-variables-and-mutability.html)
--- a/exercises/variables/variables1.rs
+++ b/exercises/variables/variables1.rs
@ -6,7 +6,9 @@
 // even after you already figured it out. If you got everything working and
 // feel ready for the next exercise, remove the `I AM NOT DONE` comment below.
 // I AM NOT DONE
 fn main() {
-    let x = 5;
+    x = 5;
    println!("x has the value {}", x);
 }
--- a/exercises/variables/variables2.rs
+++ b/exercises/variables/variables2.rs
@ -1,9 +1,10 @@
 // variables2.rs
 // Make me compile! Execute the command `rustlings hint variables2` if you want a hint :)
 // I AM NOT DONE
 fn main() {
-    let x = 10;
+    let x;
    if x == 10 {
        println!("Ten!");
    } else {
--- a/exercises/variables/variables3.rs
+++ b/exercises/variables/variables3.rs
@ -1,8 +1,10 @@
 // variables3.rs
 // Make me compile! Execute the command `rustlings hint variables3` if you want a hint :)
 // I AM NOT DONE
 fn main() {
-    let mut x = 3;
+    let x = 3;
    println!("Number {}", x);
    x = 5; // don't change this line
    println!("Number {}", x);
--- a/exercises/variables/variables4.rs
+++ b/exercises/variables/variables4.rs
@ -1,8 +1,9 @@
 // variables4.rs
 // Make me compile! Execute the command `rustlings hint variables4` if you want a hint :)
 // I AM NOT DONE
 fn main() {
-    let mut x: i32;
+    let x: i32;
    x = 512;
    println!("Number {}", x);
 }
--- a/exercises/variables/variables5.rs
+++ b/exercises/variables/variables5.rs
@ -1,9 +1,11 @@
 // variables5.rs
 // Make me compile! Execute the command `rustlings hint variables5` if you want a hint :)
 // I AM NOT DONE
 fn main() {
    let number = "T-H-R-E-E";
    println!("Spell a Number : {}", number);
-    let number = 3;
+    number = 3;
    println!("Number plus two is : {}", number + 2);
 }
--- a/exercises/variables/variables6.rs
+++ b/exercises/variables/variables6.rs
@ -1,9 +1,9 @@
 // variables6.rs
 // Make me compile! Execute the command `rustlings hint variables6` if you want a hint :)
-// consts have to have strict data type definition
+// I AM NOT DONE
-// otherwise they won't work
+
-const NUMBER: i32 = 3;
+const NUMBER = 3;
 fn main() {
    println!("Number {}", NUMBER);
 }
--- a/info.toml
+++ b/info.toml
@ -210,21 +210,6 @@ So the end goal is to:
   - since we're not creating a new vec in `main` anymore, we need to create
     a new vec in `fill_vec`, similarly to the way we did in `main`"""
 [[exercises]]
 name = "move_semantics5"
 path = "exercises/move_semantics/move_semantics5.rs"
 mode = "compile"
 hint = """
 Carefully reason about the range in which each mutable reference is in
 vogue. Does it help to update the value of referent (x) immediately after
 the mutable reference is taken? Read more about 'Mutable References'
 in the book's section References and Borrowing':
 https://doc.rust-lang.org/book/ch04-02-references-and-borrowing.html#mutable-references.
 Additional hint:
 If you can't add, change, or remove any statements in `main()`, can you
 reorder them in a way that lets the program compile?"""
 # PRIMITIVE TYPES
 [[exercises]]
@ -490,61 +475,42 @@ hint = """
 If other functions can return a `Result`, why shouldn't `main`?"""
 [[exercises]]
-name = "errors4"
+name = "errorsn"
-path = "exercises/error_handling/errors4.rs"
+path = "exercises/error_handling/errorsn.rs"
 mode = "test"
 hint = """
-`PositiveNonzeroInteger::new` is always creating a new instance and returning an `Ok` result.
+First hint: To figure out what type should go where the ??? is, take a look
-It should be doing some checking, returning an `Err` result if those checks fail, and only
+at the test helper function `test_with_str`, since it returns whatever
-returning an `Ok` result if those checks determine that everything is... okay :)"""
+`read_and_validate` returns and `test_with_str` has its signature fully
 specified.
 Next hint: There are three places in `read_and_validate` that we call a
 function that returns a `Result` (that is, the functions might fail).
 Apply the `?` operator on those calls so that we return immediately from
 `read_and_validate` if those function calls fail.
 [[exercises]]
 name = "errors5"
 path = "exercises/error_handling/errors5.rs"
 mode = "compile"
 hint = """
 Hint: There are two different possible `Result` types produced within
 `main()`, which are propagated using `?` operators. How do we declare a
 return type from `main()` that allows both?
 Another hint: under the hood, the `?` operator calls `From::from`
-on the error value to convert it to a boxed trait object, a
+on the error value to convert it to a boxed trait object, a Box<dyn error::Error>,
-`Box<dyn error::Error>`, which is polymorphic-- that means that lots of
+which is polymorphic-- that means that lots of different kinds of errors
-different kinds of errors can be returned from the same function because
+can be returned from the same function because all errors act the same
-all errors act the same since they all implement the `error::Error` trait.
+since they all implement the `error::Error` trait.
 Check out this section of the book:
 https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator
 This exercise uses some concepts that we won't get to until later in the
 course, like `Box` and the `From` trait. It's not important to understand
 them in detail right now, but you can read ahead if you like.
-Read more about boxing errors:
+Another another hint: Note that because the `?` operator returns
-https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/boxing_errors.html
+the *unwrapped* value in the `Ok` case, if we want to return a `Result` from
 `read_and_validate` for *its* success case, we'll have to rewrap a value
 that we got from the return value of a `?`ed call in an `Ok`-- this will
 look like `Ok(something)`.
 Read more about using the `?` operator with boxed errors:
 https://doc.rust-lang.org/stable/rust-by-example/error/multiple_error_types/reenter_question_mark.html
 """
-[[exercises]]
+Another another another hint: `Result`s must be "used", that is, you'll
-name = "errors6"
+get a warning if you don't handle a `Result` that you get in your
-path = "exercises/error_handling/errors6.rs"
+function. Read more about that in the `std::result` module docs:
-mode = "test"
+https://doc.rust-lang.org/std/result/#results-must-be-used"""
 hint = """
 This exercise uses a completed version of `PositiveNonzeroInteger` from
 errors4.
 Below the line that TODO asks you to change, there is an example of using
 the `map_err()` method on a `Result` to transform one type of error into
 another. Try using something similar on the `Result` from `parse()`. You
 might use the `?` operator to return early from the function, or you might
 use a `match` expression, or maybe there's another way!
 You can create another function inside `impl ParsePosNonzeroError` to use
 with `map_err()`.
 Read more about `map_err()` in the `std::result` documentation:
 https://doc.rust-lang.org/std/result/enum.Result.html#method.map_err"""
 # Generics
@ -580,7 +546,7 @@ ReportCard struct generic, but also the correct property - you will need to chan
 of the struct slightly too...you can do it!
 """
-# OPTIONS
+# OPTIONS / RESULTS
 [[exercises]]
 name = "option1"
@ -613,14 +579,13 @@ Also see Option::flatten
 """
 [[exercises]]
-name = "option3"
+name = "result1"
-path = "exercises/option/option3.rs"
+path = "exercises/error_handling/result1.rs"
-mode = "compile"
+mode = "test"
 hint = """
-The compiler says a partial move happened in the `match`
+`PositiveNonzeroInteger::new` is always creating a new instance and returning an `Ok` result.
-statement. How can this be avoided? The compiler shows the correction
+It should be doing some checking, returning an `Err` result if those checks fail, and only
-needed. After making the correction as suggested by the compiler, do
+returning an `Ok` result if those checks determine that everything is... okay :)"""
 read: https://doc.rust-lang.org/std/keyword.ref.html"""
 # TRAITS
@ -714,12 +679,7 @@ to avoid creating a copy of `numbers`, you'll need to create `child_numbers`
 inside the loop but still in the main thread.
 `child_numbers` should be a clone of the Arc of the numbers instead of a
-thread-local copy of the numbers.
+thread-local copy of the numbers."""
 This is a simple exercise if you understand the underlying concepts, but if this
 is too much of a struggle, consider reading through all of Chapter 16 in the book:
 https://doc.rust-lang.org/stable/book/ch16-00-concurrency.html
 """
 [[exercises]]
 name = "iterators1"
@ -744,38 +704,32 @@ path = "exercises/standard_library_types/iterators2.rs"
 mode = "test"
 hint = """
 Step 1
-The variable `first` is a `char`. It needs to be capitalized and added to the
+You need to call something on `first` before it can be collected
-remaining characters in `c` in order to return the correct `String`.
+Currently its type is `char`. Have a look at the methods that are available on that type:
 The remaining characters in `c` can be viewed as a string slice using the
 `as_str` method.
 The documentation for `char` contains many useful methods.
 https://doc.rust-lang.org/std/primitive.char.html
 Step 2
-Create an iterator from the slice. Transform the iterated values by applying
+First you'll need to turn the Vec into an iterator
-the `capitalize_first` function. Remember to collect the iterator.
+Then you'll need to apply your function unto each item in the vector
 P.s. Don't forget to collect() at the end!
 Step 3.
-This is surprising similar to the previous solution. Collect is very powerful
+This is very similar to the previous test. The only real change is that you will need to
-and very general. Rust just needs to know the desired type."""
+alter the type that collect is coerced into. For a bonus you could try doing this with a
 turbofish"""
 [[exercises]]
 name = "iterators3"
 path = "exercises/standard_library_types/iterators3.rs"
 mode = "test"
 hint = """
-The divide function needs to return the correct error when even division is not
+Minor hint: In each of the two cases in the match in main, you can create x with either
-possible.
+a 'turbofish' or by hinting the type of x to the compiler. You may try both.
-The division_results variable needs to be collected into a collection type.
+Major hint: Have a look at the Iter trait and at the explanation of its collect function.
-
+Especially the part about Result is interesting."""
 The result_with_list function needs to return a single Result where the success
 case is a vector of integers and the failure case is a DivisionError.
 The list_of_results function needs to return a vector of results.
 See https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.collect for how 
 the `FromIterator` trait is used in `collect()`."""
 [[exercises]]
 name = "iterators4"
@ -787,25 +741,6 @@ a mutable variable. Or, you might write code utilizing recursion
 and a match clause. In Rust you can take another functional
 approach, computing the factorial elegantly with ranges and iterators."""
 [[exercises]]
 name = "iterators5"
 path = "exercises/standard_library_types/iterators5.rs"
 mode = "test"
 hint = """
 The documentation for the std::iter::Iterator trait contains numerous methods
 that would be helpful here.
 Return 0 from count_collection_iterator to make the code compile in order to
 test count_iterator.
 The collection variable in count_collection_iterator is a slice of HashMaps. It
 needs to be converted into an iterator in order to use the iterator methods.
 The fold method can be useful in the count_collection_iterator function.
 For a further challenge, consult the documentation for Iterator to find
 a different method that could make your code more compact than using fold."""
 # THREADS
 [[exercises]]
@ -902,15 +837,7 @@ name = "clippy1"
 path = "exercises/clippy/clippy1.rs"
 mode = "clippy"
 hint = """
-Not every floating point value can be represented exactly in binary values in
+Floating point calculations are usually imprecise, so asking if two values are exactly equal is asking for trouble"""
 memory. Take a look at the description of 
 https://doc.rust-lang.org/stable/std/primitive.f32.html
 When using the binary compare operators with floating points you won't compare
 the floating point values but the binary representation in memory. This is 
 usually not what you would like to do. 
 See the suggestions of the clippy warning in compile output and use the
 machine epsilon value...
 https://doc.rust-lang.org/stable/std/primitive.f32.html#associatedconstant.EPSILON"""
 [[exercises]]
 name = "clippy2"
@ -942,19 +869,7 @@ path = "exercises/conversions/try_from_into.rs"
 mode = "test"
 hint = """
 Follow the steps provided right before the `TryFrom` implementation.
-You can also use the example at https://doc.rust-lang.org/std/convert/trait.TryFrom.html
+You can also use the example at https://doc.rust-lang.org/std/convert/trait.TryFrom.html"""
 You might want to look back at the exercise errors5 (or its hints) to remind
 yourself about how `Box<dyn Error>` works.
 If you're trying to return a string as an error, note that neither `str`
 nor `String` implements `error::Error`. However, there is an implementation
 of `From<&str>` for `Box<dyn Error>`. This means you can use `.into()` or
 the `?` operator to convert your string into the correct error type.
 If you're having trouble with using the `?` operator to convert an error string,
 recall that `?` works to convert `Err(something)` into the appropriate error
 type for returning from the function."""
 [[exercises]]
 name = "as_ref_mut"
@ -970,7 +885,4 @@ mode = "test"
 hint = """
 The implementation of FromStr should return an Ok with a Person object,
 or an Err with an error if the string is not valid.
-This is almost like the `try_from_into` exercise.
+This is almost like the `try_from_into` exercise."""
 If you're having trouble with returning the correct error type, see the
 hints for try_from_into."""
--- a/src/exercise.rs
+++ b/src/exercise.rs
@ -24,7 +24,7 @@ fn temp_file() -> String {
 }
 // The mode of the exercise.
-#[derive(Deserialize, Copy, Clone, Debug)]
+#[derive(Deserialize, Copy, Clone)]
 #[serde(rename_all = "lowercase")]
 pub enum Mode {
    // Indicates that the exercise should be compiled as a binary
@ -42,7 +42,7 @@ pub struct ExerciseList {
 // A representation of a rustlings exercise.
 // This is deserialized from the accompanying info.toml file
-#[derive(Deserialize, Debug)]
+#[derive(Deserialize)]
 pub struct Exercise {
    // Name of the exercise
    pub name: String,
--- a/src/main.rs
+++ b/src/main.rs
@ -1,7 +1,7 @@
 use crate::exercise::{Exercise, ExerciseList};
 use crate::run::run;
 use crate::verify::verify;
-use argh::FromArgs;
+use clap::{crate_version, App, Arg, SubCommand};
 use console::Emoji;
 use notify::DebouncedEvent;
 use notify::{RecommendedWatcher, RecursiveMode, Watcher};
@ -22,91 +22,85 @@ mod exercise;
 mod run;
 mod verify;
 // In sync with crate version
 const VERSION: &str = "4.4.0";
 #[derive(FromArgs, PartialEq, Debug)]
 /// Rustlings is a collection of small exercises to get you used to writing and reading Rust code
 struct Args {
    /// show outputs from the test exercises
    #[argh(switch)]
    nocapture: bool,
    /// show the executable version
    #[argh(switch, short = 'v')]
    version: bool,
    #[argh(subcommand)]
    nested: Option<Subcommands>,
 }
 #[derive(FromArgs, PartialEq, Debug)]
 #[argh(subcommand)]
 enum Subcommands {
    Verify(VerifyArgs),
    Watch(WatchArgs),
    Run(RunArgs),
    Hint(HintArgs),
    List(ListArgs),
 }
 #[derive(FromArgs, PartialEq, Debug)]
 #[argh(subcommand, name = "verify")]
 /// Verifies all exercises according to the recommended order
 struct VerifyArgs {}
 #[derive(FromArgs, PartialEq, Debug)]
 #[argh(subcommand, name = "watch")]
 /// Reruns `verify` when files were edited
 struct WatchArgs {}
 #[derive(FromArgs, PartialEq, Debug)]
 #[argh(subcommand, name = "run")]
 /// Runs/Tests a single exercise
 struct RunArgs {
    #[argh(positional)]
    /// the name of the exercise
    name: String,
 }
 #[derive(FromArgs, PartialEq, Debug)]
 #[argh(subcommand, name = "hint")]
 /// Returns a hint for the given exercise
 struct HintArgs {
    #[argh(positional)]
    /// the name of the exercise
    name: String,
 }
 #[derive(FromArgs, PartialEq, Debug)]
 #[argh(subcommand, name = "list")]
 /// Lists the exercises available in Rustlings
 struct ListArgs {
    #[argh(switch, short = 'p')]
    /// show only the paths of the exercises
    paths: bool,
    #[argh(switch, short = 'n')]
    /// show only the names of the exercises
    names: bool,
    #[argh(option, short = 'f')]
    /// provide a string to match exercise names
    /// comma separated patterns are acceptable
    filter: Option<String>,
    #[argh(switch, short = 'u')]
    /// display only exercises not yet solved
    unsolved: bool,
    #[argh(switch, short = 's')]
    /// display only exercises that have been solved
    solved: bool,
 }
 fn main() {
-    let args: Args = argh::from_env();
+    let matches = App::new("rustlings")
        .version(crate_version!())
        .author("Marisa, Carol Nichols")
        .about("Rustlings is a collection of small exercises to get you used to writing and reading Rust code")
        .arg(
            Arg::with_name("nocapture")
                .long("nocapture")
                .help("Show outputs from the test exercises")
        )
        .subcommand(
            SubCommand::with_name("verify")
                .alias("v")
                .about("Verifies all exercises according to the recommended order")
        )
        .subcommand(
            SubCommand::with_name("watch")
                .alias("w")
                .about("Reruns `verify` when files were edited")
        )
        .subcommand(
            SubCommand::with_name("run")
                .alias("r")
                .about("Runs/Tests a single exercise")
                .arg(Arg::with_name("name").required(true).index(1)),
        )
        .subcommand(
            SubCommand::with_name("hint")
                .alias("h")
                .about("Returns a hint for the current exercise")
                .arg(Arg::with_name("name").required(true).index(1)),
        )
        .subcommand(
            SubCommand::with_name("list")
                .alias("l")
                .about("Lists the exercises available in rustlings")
                .arg(
                    Arg::with_name("paths")
                        .long("paths")
                        .short("p")
                        .conflicts_with("names")
                        .help("Show only the paths of the exercises")
                )
                .arg(
                    Arg::with_name("names")
                        .long("names")
                        .short("n")
                        .conflicts_with("paths")
                        .help("Show only the names of the exercises")
                )
                .arg(
                    Arg::with_name("filter")
                        .long("filter")
                        .short("f")
                        .takes_value(true)
                        .empty_values(false)
                        .help(
                            "Provide a string to match the exercise names.\
                            \nComma separated patterns are acceptable."
                        )
                )
                .arg(
                    Arg::with_name("unsolved")
                        .long("unsolved")
                        .short("u")
                        .conflicts_with("solved")
                        .help("Display only exercises not yet solved")
                )
                .arg(
                    Arg::with_name("solved")
                        .long("solved")
                        .short("s")
                        .conflicts_with("unsolved")
                        .help("Display only exercises that have been solved")
                )
        )
        .get_matches();
-    if args.version {
+    if matches.subcommand_name().is_none() {
        println!("v{}", VERSION);
        std::process::exit(0);
    }
    if args.nested.is_none() {
        println!();
        println!(r#"       welcome to...                      "#);
        println!(r#"                 _   _ _                  "#);
@ -136,20 +130,15 @@ fn main() {
    let toml_str = &fs::read_to_string("info.toml").unwrap();
    let exercises = toml::from_str::<ExerciseList>(toml_str).unwrap().exercises;
-    let verbose = args.nocapture;
+    let verbose = matches.is_present("nocapture");
-    let command = args.nested.unwrap_or_else(|| {
+    // Handle the list command
-        let text = fs::read_to_string("default_out.txt").unwrap();
+    if let Some(list_m) = matches.subcommand_matches("list") {
-        println!("{}", text);
+        if ["paths", "names"].iter().all(|k| !list_m.is_present(k)) {
        std::process::exit(0);
    });
    match command {
        Subcommands::List(subargs) => {
            if !subargs.paths && !subargs.names {
            println!("{:<17}\t{:<46}\t{:<7}", "Name", "Path", "Status");
        }
        let filters = list_m.value_of("filter").unwrap_or_default().to_lowercase();
        let mut exercises_done: u16 = 0;
            let filters = subargs.filter.clone().unwrap_or_default().to_lowercase();
        exercises.iter().for_each(|e| {
            let fname = format!("{}", e.path.display());
            let filter_cond = filters
@ -157,20 +146,20 @@ fn main() {
                .filter(|f| !f.trim().is_empty())
                .any(|f| e.name.contains(&f) || fname.contains(&f));
            let status = if e.looks_done() {
-                    exercises_done += 1;
+                exercises_done = exercises_done + 1;
                "Done"
            } else {
                "Pending"
            };
            let solve_cond = {
-                    (e.looks_done() && subargs.solved)
+                (e.looks_done() && list_m.is_present("solved"))
-                        || (!e.looks_done() && subargs.unsolved)
+                    || (!e.looks_done() && list_m.is_present("unsolved"))
-                        || (!subargs.solved && !subargs.unsolved)
+                    || (!list_m.is_present("solved") && !list_m.is_present("unsolved"))
            };
-                if solve_cond && (filter_cond || subargs.filter.is_none()) {
+            if solve_cond && (filter_cond || !list_m.is_present("filter")) {
-                    let line = if subargs.paths {
+                let line = if list_m.is_present("paths") {
                    format!("{}\n", fname)
-                    } else if subargs.names {
+                } else if list_m.is_present("names") {
                    format!("{}\n", e.name)
                } else {
                    format!("{:<17}\t{:<46}\t{:<7}\n", e.name, fname, status)
@ -200,23 +189,41 @@ fn main() {
        std::process::exit(0);
    }
-        Subcommands::Run(subargs) => {
+    // Handle the run command
-            let exercise = find_exercise(&subargs.name, &exercises);
+    if let Some(ref matches) = matches.subcommand_matches("run") {
        let name = matches.value_of("name").unwrap();
        let matching_exercise = |e: &&Exercise| name == e.name;
        let exercise = exercises.iter().find(matching_exercise).unwrap_or_else(|| {
            println!("No exercise found for your given name!");
            std::process::exit(1)
        });
        run(&exercise, verbose).unwrap_or_else(|_| std::process::exit(1));
    }
-        Subcommands::Hint(subargs) => {
+    if let Some(ref matches) = matches.subcommand_matches("hint") {
-            let exercise = find_exercise(&subargs.name, &exercises);
+        let name = matches.value_of("name").unwrap();
        let exercise = exercises
            .iter()
            .find(|e| name == e.name)
            .unwrap_or_else(|| {
                println!("No exercise found for your given name!");
                std::process::exit(1)
            });
        println!("{}", exercise.hint);
    }
-        Subcommands::Verify(_subargs) => {
+    // Handle the verify command
    if matches.subcommand_matches("verify").is_some() {
        verify(&exercises, verbose).unwrap_or_else(|_| std::process::exit(1));
    }
-        Subcommands::Watch(_subargs) => {
+    // Handle the watch command
    if matches.subcommand_matches("watch").is_some() {
        if let Err(e) = watch(&exercises, verbose) {
            println!(
                "Error: Could not watch your progress. Error message was {:?}.",
@ -251,20 +258,22 @@ fn main() {
        println!("           ▒▒  ▒▒                      ▒▒  ▒▒         ");
        println!();
        println!("We hope you enjoyed learning about the various aspects of Rust!");
-            println!(
+        println!("If you noticed any issues, please don't hesitate to report them to our repo.");
                "If you noticed any issues, please don't hesitate to report them to our repo."
            );
        println!("You can also contribute your own exercises to help the greater community!");
        println!();
        println!("Before reporting an issue or contributing, please read our guidelines:");
        println!("https://github.com/rust-lang/rustlings/blob/main/CONTRIBUTING.md");
    }
    if matches.subcommand_name().is_none() {
        let text = fs::read_to_string("default_out.txt").unwrap();
        println!("{}", text);
    }
 }
 fn spawn_watch_shell(failed_exercise_hint: &Arc<Mutex<Option<String>>>) {
    let failed_exercise_hint = Arc::clone(failed_exercise_hint);
-    println!("Type 'hint' or open the corresponding README.md file to get help or type 'clear' to clear the screen.");
+    println!("Type 'hint' to get help or 'clear' to clear the screen");
    thread::spawn(move || loop {
        let mut input = String::new();
        match io::stdin().read_line(&mut input) {
@ -285,27 +294,6 @@ fn spawn_watch_shell(failed_exercise_hint: &Arc<Mutex<Option<String>>>) {
    });
 }
 fn find_exercise<'a>(name: &str, exercises: &'a [Exercise]) -> &'a Exercise {
    if name.eq("next") {
        exercises
            .iter()
            .find(|e| !e.looks_done())
            .unwrap_or_else(|| {
                println!("🎉 Congratulations! You have done all the exercises!");
                println!("🔚 There are no more exercises to do next!");
                std::process::exit(1)
            })
    } else {
        exercises
            .iter()
            .find(|e| e.name == name)
            .unwrap_or_else(|| {
                println!("No exercise found for '{}'!", name);
                std::process::exit(1)
            })
    }
 }
 fn watch(exercises: &[Exercise], verbose: bool) -> notify::Result<()> {
    /* Clears the terminal with an ANSI escape code.
    Works in UNIX and newer Windows terminals. */
--- a/tests/integration_tests.rs
+++ b/tests/integration_tests.rs
@ -24,7 +24,7 @@ fn fails_when_in_wrong_dir() {
 fn verify_all_success() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .arg("verify")
+        .arg("v")
        .current_dir("tests/fixture/success")
        .assert()
        .success();
@ -34,7 +34,7 @@ fn verify_all_success() {
 fn verify_fails_if_some_fails() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .arg("verify")
+        .arg("v")
        .current_dir("tests/fixture/failure")
        .assert()
        .code(1);
@ -44,7 +44,7 @@ fn verify_fails_if_some_fails() {
 fn run_single_compile_success() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .args(&["run", "compSuccess"])
+        .args(&["r", "compSuccess"])
        .current_dir("tests/fixture/success/")
        .assert()
        .success();
@ -54,7 +54,7 @@ fn run_single_compile_success() {
 fn run_single_compile_failure() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .args(&["run", "compFailure"])
+        .args(&["r", "compFailure"])
        .current_dir("tests/fixture/failure/")
        .assert()
        .code(1);
@ -64,7 +64,7 @@ fn run_single_compile_failure() {
 fn run_single_test_success() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .args(&["run", "testSuccess"])
+        .args(&["r", "testSuccess"])
        .current_dir("tests/fixture/success/")
        .assert()
        .success();
@ -74,7 +74,7 @@ fn run_single_test_success() {
 fn run_single_test_failure() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .args(&["run", "testFailure"])
+        .args(&["r", "testFailure"])
        .current_dir("tests/fixture/failure/")
        .assert()
        .code(1);
@ -84,7 +84,7 @@ fn run_single_test_failure() {
 fn run_single_test_not_passed() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .args(&["run", "testNotPassed.rs"])
+        .args(&["r", "testNotPassed.rs"])
        .current_dir("tests/fixture/failure/")
        .assert()
        .code(1);
@ -94,7 +94,7 @@ fn run_single_test_not_passed() {
 fn run_single_test_no_filename() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .arg("run")
+        .arg("r")
        .current_dir("tests/fixture/")
        .assert()
        .code(1);
@ -104,7 +104,7 @@ fn run_single_test_no_filename() {
 fn run_single_test_no_exercise() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .args(&["run", "compNoExercise.rs"])
+        .args(&["r", "compNoExercise.rs"])
        .current_dir("tests/fixture/failure")
        .assert()
        .code(1);
@ -114,7 +114,7 @@ fn run_single_test_no_exercise() {
 fn get_hint_for_single_test() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .args(&["hint", "testFailure"])
+        .args(&["h", "testFailure"])
        .current_dir("tests/fixture/failure")
        .assert()
        .code(0)
@ -131,15 +131,10 @@ fn all_exercises_require_confirmation() {
            file.read_to_string(&mut s).unwrap();
            s
        };
-        source
+        source.matches("// I AM NOT DONE").next().unwrap_or_else(|| panic!(
            .matches("// I AM NOT DONE")
            .next()
            .unwrap_or_else(|| {
                panic!(
            "There should be an `I AM NOT DONE` annotation in {:?}",
            path
-                )
+        ));
            });
    }
 }
@ -147,7 +142,7 @@ fn all_exercises_require_confirmation() {
 fn run_compile_exercise_does_not_prompt() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .args(&["run", "pending_exercise"])
+        .args(&["r", "pending_exercise"])
        .current_dir("tests/fixture/state")
        .assert()
        .code(0)
@ -158,7 +153,7 @@ fn run_compile_exercise_does_not_prompt() {
 fn run_test_exercise_does_not_prompt() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .args(&["run", "pending_test_exercise"])
+        .args(&["r", "pending_test_exercise"])
        .current_dir("tests/fixture/state")
        .assert()
        .code(0)
@ -169,7 +164,7 @@ fn run_test_exercise_does_not_prompt() {
 fn run_single_test_success_with_output() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .args(&["--nocapture", "run", "testSuccess"])
+        .args(&["--nocapture", "r", "testSuccess"])
        .current_dir("tests/fixture/success/")
        .assert()
        .code(0)
@ -180,7 +175,7 @@ fn run_single_test_success_with_output() {
 fn run_single_test_success_without_output() {
    Command::cargo_bin("rustlings")
        .unwrap()
-        .args(&["run", "testSuccess"])
+        .args(&["r", "testSuccess"])
        .current_dir("tests/fixture/success/")
        .assert()
        .code(0)
@ -197,6 +192,26 @@ fn run_rustlings_list() {
        .success();
 }
 #[test]
 fn run_rustlings_list_conflicting_display_options() {
    Command::cargo_bin("rustlings")
        .unwrap()
        .args(&["list", "--names", "--paths"])
        .current_dir("tests/fixture/success")
        .assert()
        .failure();
 }
 #[test]
 fn run_rustlings_list_conflicting_solve_options() {
    Command::cargo_bin("rustlings")
        .unwrap()
        .args(&["list", "--solved", "--unsolved"])
        .current_dir("tests/fixture/success")
        .assert()
        .failure();
 }
 #[test]
 fn run_rustlings_list_no_pending() {
    Command::cargo_bin("rustlings")
@ -216,7 +231,10 @@ fn run_rustlings_list_both_done_and_pending() {
        .current_dir("tests/fixture/state")
        .assert()
        .success()
-        .stdout(predicates::str::contains("Done").and(predicates::str::contains("Pending")));
+        .stdout(
            predicates::str::contains("Done")
                .and(predicates::str::contains("Pending"))
        );
 }
 #[test]
@ -240,3 +258,4 @@ fn run_rustlings_list_without_done() {
        .success()
        .stdout(predicates::str::contains("Done").not());
 }