This group gathers theorems of Ramsey theory and extremal combinatorics, which ask how large a structure can be before some pattern must appear, or how large a family of sets can be while avoiding a forbidden configuration. It covers results that guarantee order inside large disorder, bounds on families of sets, arithmetic progressions in colourings of the integers, and probabilistic arguments for existence. A theorem belongs here when its cited article places it in Ramsey theory, extremal combinatorics or the study of set systems.
All Ramsey Theory and Extremal Combinatorics
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De Bruijn-Erdos theorem (incidence geometry) (Wikipedia)
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In incidence geometry, the De Bruijn-Erdős theorem, originally published by Nicolaas Govert de Bruijn and Paul Erdős in 1948, states a lower bound on the number of lines determined by n points in a projective plane.
View the Source Ramsey's Theorem (Wikipedia)
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Ramsey. This initiated the combinatorial theory now called Ramsey theory, that seeks regularity amid disorder: general
View the Source Erdos-Ko-Rado Theorem (Wikipedia)
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did not publish it until 1961. It is part of the field of combinatorics, and one of the central results of extremal set
View the Source Sperner's Theorem (Wikipedia)
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in discrete mathematics, describes the largest possible families of finite sets none of which contain any other sets in the family.
View the Source Erdos-Szekeres Theorem (Wikipedia)
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result that makes precise one of the corollaries of Ramsey's theorem. While Ramsey's theorem makes it easy
View the Source Van der Waerden's Theorem (Wikipedia)
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Van der Waerden's theorem is a theorem in Ramsey theory. Van der Waerden's theorem states that for any
View the Source Lovasz local lemma (Wikipedia)
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of them occurs. This lemma is most commonly used in the probabilistic method, in particular to give existence proofs. There
View the Source Hales-Jewett Theorem (Wikipedia)
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theorem is a fundamental combinatorial result of Ramsey theory, named after Alfred W. Hales and Robert I. Jewett
View the Source Sunflower (mathematics), Wikipedia
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the latter being one of the most famous open problems of extremal combinatorics.
View the Source Erdos-Rado theorem (Wikipedia)
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the Erdős-Rado theorem is a basic result extending Ramsey's theorem to uncountable sets. It is named after
View the Source Boolean Pythagorean triples problem, Wikipedia
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The Boolean Pythagorean triples problem is a problem from Ramsey theory about whether the positive integers can be colored
View the Source Theorem on friends and strangers (Wikipedia)
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is a mathematical theorem in an area of mathematics called Ramsey theory.
View the Source Milliken's tree theorem (Wikipedia)
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in combinatorics is a partition theorem generalizing Ramsey's theorem to infinite trees, objects with more
View the Source Probabilistic Method (Wikipedia)
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In mathematics, the probabilistic method is a nonconstructive method, primarily used in
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