Category Archives: Open Problems

Dushnik-Miller for regular cardinals (part 1)

This is the first out of a series of posts on the following theorem. Theorem (Erdos-Dushnik-Miller, 1941). For every infinite cardinal λ, we have: λ(λ,ω)2. Namely, for any coloring c:[λ]2{0,1} there exists either a subset Aλ of order-type λ with … Continue reading

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The order-type of clubs in a square sequence

Recall Jensen’s notion of square: Definition (Jensen): For an infinite cardinal λ, ◻λ asserts the existence of a sequence C=Cααacc(λ+) such that for every limit α<λ+: Cα is a club subset of α of order-type λ; if βacc(Cα), … Continue reading

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Jensen’s diamond principle and its relatives

This is chapter 6 in the book Set Theory and Its Applications (ISBN: 0821848127). Abstract: We survey some recent results on the validity of Jensen’s diamond principle at successor cardinals. We also discuss weakening of this principle such as club … Continue reading

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