Thrush is the "T combinator" - I believe that the "Thrush" name comes from To Mock a Mockingbird by Raymond Smullyan [1].

[1]: https://www.amazon.com/Mock-Mockingbird-Other-Logic-Puzzles/...

[2]: https://en.wikipedia.org/wiki/Combinatory_logic#In_computing

[3]: https://leanpub.com/combinators/read#leanpub-auto-the-thrush

To Mock a Mockingbird was a book that was sent to me and I enjoyed it. I can't fully do all of the puzzles, but they are for sure fun.

https://www.amazon.com/Mock-Mockingbird-Raymond-Smullyan/dp/...

As has been noted repeatedly: “To Mock a Mockingbird” by Raymond Smullyan. It’s one of the finest mathematics/logic books ever written for the intelligent layman.

http://www.amazon.com/gp/product/0192801422?ie=UTF8&tag=...

(Yes, that’s an affiliate code. Strip it out and replace with your favourite charity. “Raganwald" is an acceptable answer for “favourite charity.”)