Wegner's conjecture on good covers

Let a good cover in Rd\mathbb{R}^d be a collection of open sets such that every subcollection has intersection either empty or homeomorphic to an open dd-ball. The nerve of a collection is the simplicial complex whose vertices are the sets and whose faces are the subcollections with nonempty intersection. A finite simplicial complex is topologically dd-representable if it is isomorphic to the nerve of a good cover in Rd\mathbb{R}^d. A simplicial complex is dd-collapsible if it can be reduced to the empty complex by repeatedly removing a face of dimension at most d1d-1 contained in a unique maximal face. Wegner's conjecture. Every topologically dd-representable simplicial complex is dd-collapsible. This conjecture proposes a topological extension of Wegner's theorem that every convexly dd-representable simplicial complex is dd-collapsible; the paper gives a counterexample, so the conjecture is refuted.

Sources & referencesView supporting material

Primary source

Martin Tancer, “A counterexample to Wegner's conjecture on good covers”, arXiv:1008.1895 (2010).

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