Two kinds of fixed point theorems and reverse mathematics
Weiguang Peng, Takeshi Yamazaki · Mathematical logic quarterly · 2017
Abstract In this paper, we investigate the logical strength of two types of fixed point theorems in the context of reverse mathematics. One is concerned with extensions of the Banach contraction principle. Among theorems in this type, we mainly show that the Caristi fixed point theorem is equivalent to over . The other is dedicated to topological fixed point theorems such as the Brouwer fixed point theorem. We introduce some variants of the Fan‐Browder fixed point theorem and the Kakutani fixed point theorem, which we call and , respectively. Then we show that is equivalent to and is equivalent to , over . In addition, we also study the application of the Fan‐Browder fixed point theorem to game systems.