English

Brouwer fixed point theorem as a corollary of Lawvere

Logic 2020-05-21 v2

Abstract

It is investigated in what sense the Brouwer fixed point theorem may be viewed as a corollary of the Lawvere fixed point theorem. A suitable generalisation of the Lawvere fixed point theorem is found and a means is identified by which the Brouwer fixed point theorem can be shown to be a corollary, once an appropriate continuous surjective mapping AXAA' \rightarrow X^{A''} has been constructed for each space XX in a certain class of "nice" spaces for each one of which the exponential topology on XAX^{A''} exists, and here AA' and AA'' have the same carrier set and the topology on AA' is finer than on AA''. It is shown that there is a certain natural way of attempting to derive Brouwer as a corollary of Lawvere which is not possible, that is there is no space AA for which the exponential topology on [0,1]A[0,1]^{A} exists and there is a continuous surjection A[0,1]AA \rightarrow [0,1]^{A}. We then examine the range of contexts in which phenomena like those described in the first result occur, from a broadly model-theoretic perspective, with a view towards applications for the original motivation for the problem as a problem in decision theory for AI systems, suggested by the Machine Intelligence Research Institute.

Keywords

Cite

@article{arxiv.2005.01563,
  title  = {Brouwer fixed point theorem as a corollary of Lawvere},
  author = {Rupert McCallum},
  journal= {arXiv preprint arXiv:2005.01563},
  year   = {2020}
}