Copy-paste the code from `conceptual_semantics.lean` to [Lean 4 web editor](https://live.lean-lang.org/) and see whether everything checks out.

OR

1. Install Lean 4 and VS Code following
   these [instructions](https://leanprover-community.github.io/get_started.html).

2. Make sure you have [git](https://git-scm.com/) installed.

3. Follow these [instructions](https://leanprover-community.github.io/install/project.html#working-on-an-existing-project)
   to fetch the `mathematics_in_lean` repository and open it up in VS Code.

4. Drop `conceptual_semantics.lean` file into the cloned folder and open the folder in VS Code.

5. Click on the `conceptual_semantics.lean` file to open it up and see whether everything checks out.
