This is the work in progress port of mathlib to Lean 4.

A guide on how to port a file from mathlib3 to mathlib4 can be found in the wiki. The porting effort is coordinated through zulip, if you want to contribute to the port please come to the mathlib4 stream.

• Make sure Lean is not running, and close all instances of VSCode running Lean processes.
• Get the newest version of elan. If you already have installed a version of Lean, you can run

  elan self update
  

  If the above command fails, or if you need to install elan, run

  curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf | sh
  

  If this also fails, follow the instructions under Regular install here.
• To build mathlib4 run lake build. To build and run all tests, run make.
• You can use lake build +Mathlib.Import.Path to build a particular file, e.g. lake build +Mathlib.Algebra.Group.Defs.
• If you added a new file, run the following command to update Mathlib.lean

  find Mathlib -name "*.lean" | env LC_ALL=C sort | sed 's/\.lean//;s,/,.,g;s/^/import /' > Mathlib.lean
  

Run lake exe cache get to download cached build files that are computed by mathlib4's automated workflow. If tar terminates with an error, it means that you might have ended up with corrupted files. In this case, run lake exe cache get! to overwrite them (get won't try to download the same file again).

Call lake exe cache to see its help menu.

Building HTML documentation locally is straightforward:

lake -Kdoc=on build Mathlib:docs

The HTML files can then be found in build/doc.

If you want to update dependencies, use lake update -Kdoc=on. This will update the lean_packages/manifest.json file correctly. You will need to make a PR after committing the changes to this file.

If you want to start a project that uses mathlib4 as a dependency, you can run:

lake new MyProject math

Important: the command above requires a more recent toolchain set as default, which can be done with, for example:

elan default leanprover/lean4:nightly-2023-02-04

Or, if you already have a project and you want to be able to use mathlib4, add these lines to your lakefile.lean:

require mathlib4 from git
  "https://github.com/leanprover-community/mathlib4" @ "<REVISION>"

Where <REVISION> can be a commit hash, a branch or a tag. You can check this section from Lake's README for more info.

Either way, make sure that your project uses the same Lean 4 toolchain as the one used in mathlib4.

Lake projects inherit executables declared with lean_exe from their dependencies. It means that you can call lake exe cache on your project if you're using mathlib4 as a dependency. However, make sure to follow these guidelines:

• Call lake exe cache get (or other cache commands) from the root directory of your project
• If your project depends on std4 or quote4, let mathlib4 pull them transitively. That is, don't require them on your lakefile.lean