Proof mining and combinatorics : Program extraction for Ramsey's theorem for pairs

Abstract

In this thesis we give a proof-theoretic account of the strength of Ramsey's theorem for pairs and related principles. We develop a method to extract programs from proofs using this theorem. Moreover, we consider the strength of different variants of the Bolzano-Weierstras principle. We show that Ramsey's theorem for pairs implies a variant of the Bolzano-Weierstras principle and, hence, show that our program extraction method is applicable to proofs using this principle. Also, we develop a method to extract programs from proofs that use non-principal ultrafilters and along with this we obtain a conservation result for the statement that a non-principal ultrafilter exists. This method is based on the techniques we developed for Ramsey's theorem for pairs.