Reimer's condition conjecture

Let [n]={1,,n}[n]=\{1,\ldots,n\}, let A2[n]{\mathcal A}\subseteq 2^{[n]}, and suppose A{\mathcal A} satisfies Condition 1: there is a filter F2[n]{\mathcal F}\subseteq 2^{[n]} and a bijection AFAA\mapsto F_A from A{\mathcal A} to F{\mathcal F} such that AFAA\subseteq F_A for every AAA\in{\mathcal A} and [A,FA][B,FB]=[A,F_A]\cap[B,F_B]=\emptyset for distinct A,BAA,B\in{\mathcal A}, where [A,B]={C:ACB}[A,B]=\{C:A\subseteq C\subseteq B\}. Reimer's condition conjecture. There is an element x[n]x\in[n] that belongs to at least half the sets of A{\mathcal A}. The conjecture asks whether Reimer's sufficient condition alone implies the conclusion of the union-closed sets conjecture. The paper's abstract states that this implication is false, so the conjecture is refuted.

Sources & referencesView supporting material

Primary source

Abigail Raz, “Note on the union-closed sets conjecture”, arXiv:1704.07022 (2017).

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