Absolutely Choiceless Proofs

Abstract

We study a well-known technique of using absoluteness for giving choice-free proofs to some statements which are known to be provable with the axiom of choice. The idea is to reduce the problem to an inner model where the axiom of choice holds and use absoluteness. We examine the complexity of the sentences that this technique can be applied to, and show that many of the theorems in basic partition calculus have the adequate complexity for this technique to apply.