The paper introduces the notion of a (K, b)-free cover, where K is a forbidden homological minor of the ambient space U and the reduced Betti numbers of the intersections are bounded by b. The main results are:
The fractional Helly number of a (K, b)-free cover is at most µ(K) + 1, where µ(K) is the maximum sum of the dimensions of two disjoint faces in K.
The assertion of the (p, q)-theorem holds for every p ≥ q > µ(K) and every (K, b)-free cover F. This improves upon previous results that required p ≥ q ≥ m, where m is a very large number obtained by successive iterations of Ramsey's theorem.
The proofs use Ramsey-type arguments combined with the notion of stair convexity to construct (forbidden) homological minors in cubical complexes. The paper also discusses connections to topological Helly theorems, stepping-up in combinatorial convexity, and homological VC-dimension.
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