Where is the Godel-point hiding: Gentzen's Consistency Proof of 1936 and His Representation of Constructive Ordinals

This book explains the first published consistency proof of PA. It contains the original Gentzen''s proof, but it uses modern terminology and examples to illustrate the essential notions. The author comments on Gentzen''s steps which are supplemented with exact calculations and parts of formal derivations. A notable aspect of the proof is the representation of ordinal numbers that was developed by...