Tag Archives: Dushnik-Miller

Dushnik-Miller for regular cardinals (part 3)

Here is what we already know about the Dushnik-Miller theorem in the case of ω1 (given our earlier posts on the subject): ω1(ω1,ω+1)2 holds in ZFC; ω1(ω1,ω+2)2 may consistently fail; ω1(ω1,ω1)2 fails in ZFC. In this post, we shall provide … Continue reading

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Dushnik-Miller for singular cardinals (part 2)

In the first post on this subject, we provided a proof of λ(λ,ω+1)2 for every regular uncountable cardinal λ. In the second post, we provided a proof of λ(λ,ω)2 for every singular cardinal λ, and showed that λ(λ,ω+1)2 fails for every … Continue reading

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Dushnik-Miller for regular cardinals (part 2)

In this post, we shall provide a proof of Todorcevic’s theorem, that b=ω1 implies ω1(ω1,ω+2)2. This will show that the Erdos-Rado theorem that we discussed in an earlier post, is consistently optimal. Our exposition of Todorcevic’s theorem would be … Continue reading

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Dushnik-Miller for singular cardinals (part 1)

Continuing the previous post, let us now prove the following. Theorem (Erdos-Dushnik-Miller, 1941). For every singular cardinal λ, we have: λ(λ,ω)2. Proof. Suppose that λ is a singular cardinal, and c:[λ]2{0,1} is a given coloring. For any ordinal α<λ, denote … Continue reading

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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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