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I see that author used these Combinator Birds or Birbs [1]. [1] https://www.angelfire.com/tx4/cus/combinator/birds.html https://www.angelfire.com/tx4/cus/combi

I see that author used these Combinator Birds or Birbs [1]. [1] https://www.angelfire.com/tx4/cus/combinator/birds.html https://www.angelfire.com/tx4/cus/combinator/birds.html

ufo 3y ago
Which goes back to Raymond Smullyan: https://en.wikipedia.org/wiki/To_Mock_a_Mockingbird https://en.wikipedia.org/wiki/To_Mock_a_Mockingbird