Gentzen (1936): PA is consistent, proved by transfinite induction up to the ordinal ε₀ — outside PA by the second incompleteness theorem. Foundational for proof-theoretic ordinal analysis.
Gentzen (1936): PA is consistent, proved by transfinite induction up to the ordinal ε₀ — outside PA by the second incompleteness theorem. Foundational for proof-theoretic ordinal analysis.