Gödel's Reformulation of Gentzen's First Consistency Proof For Arithmetic: The No-Counterexample Interpretation

The last section of “Lecture at Zilsel's” [9, §4] contains an interesting but quite condensed discussion of Gentzen's first version of his consistency proof for PA [8], reformulating it as what has come to be called the no-counterexample interpretation . I will describe Gentzen's result (in game-theoretic terms), fill in the details (with some corrections) of Godel's reformulation, and discuss the relation between the two proofs.