Distributive Lattices, Bipartite Graphs and Alexander Duality

  • Authors:
  • Jürgen Herzog;Takayuki Hibi

  • Affiliations:
  • Fachbereich Mathematik und Informatik, Universität Duisburg-Essen, Essen, Germany 45117;Department of Pure and Applied Mathematics, Graduate School of Information Science and Technology, Osaka University, Toyonaka, Osaka, Japan 560-0043

  • Venue:
  • Journal of Algebraic Combinatorics: An International Journal
  • Year:
  • 2005

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Abstract

A certain squarefree monomial ideal HP arising from a finite partially ordered set P will be studied from viewpoints of both commutative algbera and combinatorics. First, it is proved that the defining ideal of the Rees algebra of HP possesses a quadratic Gröbner basis. Thus in particular all powers of HP have linear resolutions. Second, the minimal free graded resolution of HP will be constructed explicitly and a combinatorial formula to compute the Betti numbers of HP will be presented. Third, by using the fact that the Alexander dual of the simplicial complex 驴 whose Stanley---Reisner ideal coincides with HP is Cohen---Macaulay, all the Cohen---Macaulay bipartite graphs will be classified.