BSL
2004
13 years 11 months ago
2004
Frege Arithmetic (FA) is the second-order theory whose sole non-logical axiom is Hume's Principle, which says that the number of Fs is identical to the number of Gs if and on...
AML
2008
13 years 11 months ago
2008
Leo Harrington showed that the second-order theory of arithmetic WKL0 is 1 1-conservative over the theory RCA0. Harrington's proof is model-theoretic, making use of a forcing...