Combinatorics: set systems, hypergraphs, families of vectors, and combinatorial probability
Combinatorics: set systems, hypergraphs, families of vectors, and combinatorial probability
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Let A be a family of subsets of an n-set such that A does not contain distinct sets A and B with |A@?B|=2|B@?A|. How large can A be? Our aim in this note is to determine the maximum size of such an A. This answers a question of Kalai. We also give some related results and conjectures.