On exact blockers and anti-blockers, Δ-conjecture, and related problems

  • Authors:
  • Vladimir Gurvich

  • Affiliations:
  • -

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2011

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Abstract

Let us consider two binary systems of inequalities (i) Cx=e and (ii) Cx@?e, where C@?{0,1}^m^x^n is an mxn(0,1)-matrix, x@?{0,1}^n, and e is the vector of m ones. The set of all support-minimal (respectively, support-maximal) solutions x to (i) (respectively, to (ii)) is called the blocker (respectively, anti-blocker). A blocker B (respectively, anti-blocker A) is called exact if Cx=e for every x@?B (respectively, x@?A). Exact blockers can be completely characterized. There is a one-to-one correspondence between them and P"4-free graphs (along with a well-known one-to-one correspondence between the latter and the so-called read-once Boolean functions). However, the class of exact anti-blockers is wider and more sophisticated. We demonstrate that it is closely related to the so-called CIS graphs, more general @?-CIS d-graphs, and @D-conjecture.