The proof-theoretic ordinal of Peano Arithmetic is Epsilon-0

Published: Dec. 11, 2021, 4 a.m.

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In this episode, I outline the argument for why the proof-theoretic ordinal (in the sense of Rathjen, as presented last episode) is epsilon-0.\\xa0 My explanation has something of a hole, in explaining how one would go about deriving induction for ordinals strictly less than epsilon-0 in Peano Arithmetic.\\xa0 To help paper over this hole a little, I discuss a really nice recent exposition of encoding ordinals in Agda.

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