English

A Vietoris-Smale mapping theorem for the homotopy of hyperdefinable sets

Logic 2017-06-08 v1

Abstract

Results of Smale (1957) and Dugundji (1969) allow to compare the homotopy groups of two topological spaces XX and YY whenever a map f:XYf:X\to Y with strong connectivity conditions on the fibers is given. We apply similar techniques in o-minimal expansions of fields to compare the o-minimal homotopy of a definable set XX with the homotopy of some of its bounded hyperdefinable quotients X/EX/E. Under suitable assumption, we show that πn(X)defπn(X/E)\pi_{n}(X)^{\rm def}\cong\pi_{n}(X/E) and dim(X)=dimR(X/E)\dim(X)=\dim_{\mathbb R}(X/E). As a special case, given a definably compact group, we obtain a new proof of Pillay's group conjecture "dim(G)=dimR(G/G00\dim(G)=\dim_{\mathbb R}(G/G^{00})" largely independent of the group structure of GG. We also obtain different proofs of various comparison results between classical and o-minimal homotopy.

Keywords

Cite

@article{arxiv.1706.02094,
  title  = {A Vietoris-Smale mapping theorem for the homotopy of hyperdefinable sets},
  author = {Alessandro Achille and Alessandro Berarducci},
  journal= {arXiv preprint arXiv:1706.02094},
  year   = {2017}
}

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24 pages