2007 | OriginalPaper | Chapter
The Union of Minimal Hitting Sets: Parameterized Combinatorial Bounds and Counting
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We study how many vertices in a rank-
r
hypergraph can belong to the union of all inclusion-minimal hitting sets of at most
k
vertices. This union is interesting in certain combinatorial inference problems with hitting sets as hypotheses, as it provides a problem kernel for likelihood computations (which are essentially counting problems) and contains the most likely elements of hypotheses. We give worst-case bounds on the size of the union, depending on parameters
r
,
k
and the size
k
*
of a minimum hitting set. (Note that
k
≥
k
*
is allowed.) Our result for
r
= 2 is tight. The exact worst-case size for any
r
≥ 3 remains widely open. By several hypergraph decompositions we achieve nontrivial bounds with potential for further improvements.