Idempotents in Semigroups
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Transcript of Idempotents in Semigroups
Idempotents in compact Idempotents in compact semigroups and Ramsey semigroups and Ramsey
TheoryTheory
Complete disorder is Complete disorder is impossibleimpossible
T.S.MotzkinT.S.Motzkin
Piegenhole principlePiegenhole principle
If m objects are some colored with n colors and If m objects are some colored with n colors and m>n then two objects have the same color.m>n then two objects have the same color.
Schur’s theorem (1916)Schur’s theorem (1916)
zy that xso ,color same thehaving
N, zy,exist x, thereN of coloring-r allFor
Van der Waerden’s Theorem (1927)Van der Waerden’s Theorem (1927)
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nprogressio arithmetic ticmonochroma a
exists therecolored-r is N if ,r l, all
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Ramsey’s Theorem (Ramsey’s Theorem (1930,finite 1930,finite versionversion))
Let r,k,l be given integers. Then there is a Let r,k,l be given integers. Then there is a positive integer n with the following property.If positive integer n with the following property.If the k-subsets of an n-set are colored with r the k-subsets of an n-set are colored with r colors,then there is a monochromatic l-set i.e colors,then there is a monochromatic l-set i.e one all of whose k-sets have the same color.one all of whose k-sets have the same color.
Ramsey’s theorem (Ramsey’s theorem (infinite forminfinite form))
Let X be an infinite set, and k and r positive Let X be an infinite set, and k and r positive integers. Suppose that the k-subsets of X are integers. Suppose that the k-subsets of X are colored with r colors. Then there is an infinite colored with r colors. Then there is an infinite subset Y of X, all of whose k-subsets have the subset Y of X, all of whose k-subsets have the same color.same color.
Definition .Definition .
} S ofnumber finite afor 1 ; 1,0 ; {FS(A)
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sss
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Folkman’s TheoremFolkman’s Theorem
If N is finitely colored there exist If N is finitely colored there exist arbitrarily large finite sets A such that arbitrarily large finite sets A such that FS(A) is monochromatic.FS(A) is monochromatic.
Hindman’s TheoremHindman’s Theorem
If N is finitely colored there exists If N is finitely colored there exists infinite such that FS(S) is infinite such that FS(S) is monochromatic.monochromatic.
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