A glimpse of Lean
This repository is an introduction to theorem proving in Lean for the impatient. The goal is to get a feel for what proving in Lean looks like in 2 or 3 hours, or maybe devote half a day or a full day.
There are two tracks. Both start with reading the Introduction.lean file.
Then the short track continues in the Shorter.lean file which is meant to give
you access to not completely empty mathematical proofs in two hours if you are
ready to move pretty fast.
If you have a bit more time, you should instead read explanations and do
exercises in the Basics folder, and then choose to work on one file from the
Topics folder. Of course, you can play with all files from that folder if you
have even more time.
To work using Lean, you either have to install Lean locally, or use a lean4web server, or use Codespaces or use Gitpod.
Online version, no registration
If you don’t want to install Lean and don’t want to create an account on any website, you can use the lean4web server hosted by the Lean FRO as follows:
- read the introduction file
- then read and edit the explanations and exercises file
You can refer to the tactics cheatsheet while doing the exercises. Tactics are explained in the Lean file, but the pdf can be more convenient as a reference.
Online version, with registration
There are also websites that are a bit more comfortable but require creating a GitHub account.
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To use codespaces, make sure you’re logged in to GitHub, click the button below, select
4-core, and then pressCreate codespace. After a few minutes an editor with Lean working will open in your browser.
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Gitpod is very similar to Codespaces, click the button below, press
Continueand wait a few minutes.
Local installation
If you want the full luxury Lean experience, you should install it on your computer.
For this you can follow the instructions here.
If you have a lot more time, you should read the book Mathematics in Lean.