I especially like the Turing / Godel equivalency stuff he discusses.
[1] https://arxiv.org/pdf/math/0404335.pdf
https://tromp.github.io/cl/Binary_lambda_calculus.html
This has recently led to a functional Busy Beaver at
https://mathoverflow.net/questions/353514/whats-the-smallest...
https://oeis.org/A333479
I especially like the Turing / Godel equivalency stuff he discusses.
[1] https://arxiv.org/pdf/math/0404335.pdf