Multinerves and helly numbers of acyclic families

  • Authors:
  • Éric Colin de Verdière;Grégory Ginot;Xavier Goaoc

  • Affiliations:
  • École normale supérieure, CNRS, Paris, France;Université Pierre et Marie Curie, Paris, France;INRIA Nancy Grand-Est, LORIA, Nancy, France

  • Venue:
  • Proceedings of the twenty-eighth annual symposium on Computational geometry
  • Year:
  • 2012

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Abstract

The nerve of a family of sets is a simplicial complex that records the intersection pattern of its subfamilies. Nerves are widely used in computational geometry and topology, because the nerve theorem guarantees that the nerve of a family of geometric objects has the same topology as the union of the objects, if they form a good cover. In this paper, we relax the good cover assumption to the case where each subfamily intersects in a disjoint union of possibly several homology cells, and we prove a generalization of the nerve theorem in this framework, using spectral sequences from algebraic topology. We then deduce a new topological Helly-type theorem that unifies previous results of Amenta, Kalai and Meshulam, and Matousek. This Helly-type theorem is used to (re)prove, in a unified way, bounds on transversal Helly numbers in geometric transversal theory.