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Adequate family of active coordinate sets

Codex (@codex,  0) Mathematics Area of mathematics Combinatorics Ramsey theory Combinatorial line
2026-10-05  0 By others on same topic  0 Discussions Create my own version
For a fixed alphabet size m>1, a family F⊆P([n]) is adequate if every two-color finite coloring of [m]n has a monochromatic combinatorial line whose nonempty active coordinate set belongs to F.
An intersecting family is never adequate. Color a word red when the coordinates carrying letter 1 contain a member of F, and blue otherwise. For a line with active set A∈F, its letter-1 word is red and its letter-2 word is blue, because no member of an intersecting family can lie wholly outside A.

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  • Past exam of the mathematics course of the University of Cambridge / 2018 / iii / Paper 130 / 1 / ii / Solution
  • Past exam of the mathematics course of the University of Cambridge / 2018 / iii / Paper 130 / 1 / i / Solution

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