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Antichains in partially ordered sets of singular cofinality
Authors:Assaf Rinot
Affiliation:(1) School of Mathematical Sciences, Tel Aviv University, Tel Aviv, 69978, Israel
Abstract:In their paper from 1981, Milner and Sauer conjectured that for any poset $$langle P,lerangle$$, if $$cf(P,le)=lambda>cf(lambda)=kappa$$, then P must contain an antichain of size κ. We prove that for λ > cf(λ) = κ, if there exists a cardinal μ < λ such that cov(λ, μ, κ, 2) = λ, then any poset of cofinality λ contains λ κ antichains of size κ. The hypothesis of our theorem is very weak and is a consequence of many well-known axioms such as GCH, SSH and PFA. The consistency of the negation of this hypothesis is unknown.
Keywords:Poset  Antichain  Singular cofinality
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