Note: Combinatorial Alexander Duality—A Short and Elementary Proof

  • Authors:
  • Anders Björner;Martin Tancer

  • Affiliations:
  • Royal Institute of Technology, Department of Mathematics, 100 44, Stockholm, Sweden;Charles University, Department of Applied Mathematics, Faculty of Mathematics and Physics, Malostranské Náměstí 25, 118 00, Prague, Czech Republic

  • Venue:
  • Discrete & Computational Geometry
  • Year:
  • 2009

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Abstract

Let X be a simplicial complex with ground set V. Define its Alexander dual as the simplicial complex X *={σ⊆V∣V∖σ ∉ X}. The combinatorial Alexander duality states that the ith reduced homology group of X is isomorphic to the (|V|−i−3)th reduced cohomology group of X * (over a given commutative ring R). We give a self-contained proof from first principles accessible to a nonexpert.