English

Computable counter-examples to the Brouwer fixed-point theorem

General Mathematics 2008-04-22 v1

Abstract

This paper is an overview of results that show the Brouwer fixed-point theorem (BFPT) to be essentially non-constructive and non-computable. The main results, the counter-examples of Orevkov and Baigger, imply that there is no procedure for finding the fixed point in general by giving an example of a computable function which does not fix any computable point. Research in reverse mathematics has shown the BFPT to be equivalent to the weak K\"onig lemma in RCA0_0 (the system of recursive comprehension) and this result is illustrated by relating the weak K\"onig lemma directly to the Baigger example.

Keywords

Cite

@article{arxiv.0804.3199,
  title  = {Computable counter-examples to the Brouwer fixed-point theorem},
  author = {Petrus H. Potgieter},
  journal= {arXiv preprint arXiv:0804.3199},
  year   = {2008}
}

Comments

10 pages; to appear in local proceedings of Computability in Europe 2008: Logic and Theory of Algorithms

R2 v1 2026-06-21T10:32:53.433Z