# References

1. [Mathematics in Lean by Jeremy Avigad and Patrick Massot](https://leanprover-community.github.io/mathematics_in_lean/mathematics_in_lean.pdf)
2. [The Mathlib 4 API docs](https://leanprover-community.github.io/mathlib4_docs/)
3. [The Lean Zulip Chat](https://leanprover.zulipchat.com/)
4. [Some Lean Games](https://adam.math.hhu.de/)
5. [The original version of The Natural Number Game](https://www.ma.imperial.ac.uk/~buzzard/xena/natural_number_game/index2.html)