First 21 minutes of the recording are setup and waiting for folks to arrive.
Whenever I see intros of the Lambda Calculus, I always feel the need to recommend the late Jim Weitrich’s “Y Not”: https://www.youtube.com/watch?v=FITJMJjASUs.
I cannot recommend it enough. In it, Jim covers the same example problem as Gary does (the recursive factorial function), but he does not gloss over the Y Combinator; in fact, Jim derives the Y Combinator on-stage step-by-step after giving clear examples of functional refactoring. Personally, it (along Tom Stuart’s “Programming with Nothing” talk) is one of my favorite introductions to λ calculus.
Corey Haines also gave a good talk along those lines. https://www.youtube.com/watch?v=QPqoFCHpLF4 I like Corey’s approach and find it a nice complement to Jim’s talk.