Discussed here: https://news.ycombinator.com/item?id=31334617 https://news.ycombinator.com/item?id=31334617 (I was just looking it up because I had misrecalled

Discussed here: https://news.ycombinator.com/item?id=31334617 https://news.ycombinator.com/item?id=31334617 (I was just looking it up because I had misrecalled that discussion as being on Keenan's paper) And the origin of the bird-themed combinators for both: https://en.wikipedia.org/wiki/To_Mock_a_Mockingbird https://en.wikipedia.org/wiki/To_Mock_a_Mockingbird To Mock a Mockingbird by Smullyan (on my shelf to read, but not yet read)