* References
:PROPERTIES:
:CUSTOM_ID: references
:END:
** Primary Learning Resources
:PROPERTIES:
:CUSTOM_ID: primary-learning-resources
:END:
| Abbr | Title                            | Link                                                        |
|------+----------------------------------+-------------------------------------------------------------|
| FPIL | /Functional Programming in Lean/ | https://lean-lang.org/functional_programming_in_lean/       |
| TPIL | /Theorem Proving in Lean 4/      | https://leanprover.github.io/theorem_proving_in_lean4/      |
| MiL  | /Mathematics in Lean/            | https://leanprover-community.github.io/mathematics_in_lean/ |

** PL Semantics Formalizations in Lean 4
:PROPERTIES:
:CUSTOM_ID: pl-semantics-formalizations-in-lean-4
:END:
| Resource                | What it covers                                                        | Link                                       |
|-------------------------+-----------------------------------------------------------------------+--------------------------------------------|
| syndikos/lean4-stlc     | STLC: syntax, semantics, typing, metatheory (Progress + Preservation) | https://github.com/syndikos/lean4-stlc     |
| chenson2018/LeanScratch | Untyped λ-calculus: de Bruijn + locally nameless, confluence proofs   | https://github.com/chenson2018/LeanScratch |
| sdemos/type-inference   | STLC + HM type inference, soundness & completeness of W               | https://github.com/sdemos/type-inference   |
| rami3l/PLFaLean         | PLFA Parts 2--3 translated to Lean 4                                  | https://github.com/rami3l/PLFaLean         |

** PL Theory (Non-Lean)
:PROPERTIES:
:CUSTOM_ID: pl-theory-non-lean
:END:
| Resource                                                        | Format    | Link                                                                     |
|-----------------------------------------------------------------+-----------+--------------------------------------------------------------------------|
| Software Foundations Vol.2                                      | Rocq book | https://softwarefoundations.cis.upenn.edu/                               |
| PLFA Part 2                                                     | Agda book | https://plfa.github.io/                                                  |
| Chris Henson: Beginner Resources for Formalizing Lambda Calculi | Blog post | https://chrishenson.net/posts/2025-05-10-formalized_lambda_calculus.html |

** HM Type System
:PROPERTIES:
:CUSTOM_ID: hm-type-system
:END:
| Resource                                                                   | Format     | Link                                                             |
|----------------------------------------------------------------------------+------------+------------------------------------------------------------------|
| Wikipedia: Hindley-Milner type system                                      | Reference  | https://en.wikipedia.org/wiki/Hindley%E2%80%93Milner_type_system |
| Jeff Vaughan: "A proof of correctness for the HM type inference algorithm" | PDF (2008) | https://www.jeffvaughan.net/docs/hmproof.pdf                     |

** Community
:PROPERTIES:
:CUSTOM_ID: community
:END:
- Official site: https://lean-lang.org/
- Zulip chat: https://leanprover.zulipchat.com/
- Lean 4 docs: https://lean-lang.org/documentation/