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A Bipartite Analogue of Dilworth’s Theorem

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Abstract

Let m(n) be the maximum integer such that every partially ordered set P with n elements contains two disjoint subsets A and B, each with cardinality m(n), such that either every element of A is greater than every element of B or every element of A is incomparable with every element of B. We prove that \(m(n)=\Theta\left(\frac{n}{\log n}\right)\). Moreover, for fixed ε ∈ (0,1) and n sufficiently large, we construct a partially ordered set P with n elements such that no element of P is comparable with \(n^{\varepsilon } \) other elements of P and for every two disjoint subsets A and B of P each with cardinality at least \(\frac{14n}{\epsilon\log_2 n}\), there is an element of A that is comparable with an element of B.

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  1. Massachusetts Institute of Technology, Cambridge, MA, 02139, USA

    Jacob Fox

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Fox, J. A Bipartite Analogue of Dilworth’s Theorem. Order 23, 197–209 (2006). https://doi.org/10.1007/s11083-006-9043-z

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