Tag Archives: Singular cardinals combinatorics

Ramsey theory over partitions II: Negative Ramsey relations and pump-up theorems

Joint work with Menachem Kojman and Juris Steprāns. Abstract. In this series of papers, we advance Ramsey theory of colorings over partitions. In this part, we concentrate on anti-Ramsey relations, or, as they are better known, strong colorings, and in … Continue reading

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Sigma-Prikry forcing II: Iteration Scheme

Joint work with Alejandro Poveda and Dima Sinapova. Abstract. In Part I of this series, we introduced a class of notions of forcing which we call Σ-Prikry, and showed that many of the known Prikry-type notions of forcing that centers … Continue reading

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Sigma-Prikry forcing I: The Axioms

Joint work with Alejandro Poveda and Dima Sinapova. Abstract. We introduce a class of notions of forcing which we call Σ-Prikry, and show that many of the known Prikry-type notions of forcing that centers around singular cardinals of countable cofinality … Continue reading

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More notions of forcing add a Souslin tree

Joint work with Ari Meir Brodsky. Abstract.   An 1-Souslin tree is a complicated combinatorial object whose existence cannot be decided on the grounds of ZFC alone. But 15 years after Tennenbaum and independently Jech devised notions of forcing for introducing … Continue reading

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Ordinal definable subsets of singular cardinals

Joint work with James Cummings, Sy-David Friedman, Menachem Magidor, and Dima Sinapova. Abstract. A remarkable result by Shelah states that if κ is a singular strong limit cardinal of uncountable cofinality then there is a subset x of κ such … 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 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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On topological spaces of singular density and minimal weight

Abstract: We introduce a weakening of the Generalized Continuum Hypothesis, which we will refer to as the Prevalent Singular cardinals Hypothesis (PSH), and show it implies that every topological space of density and weight ω1 is not hereditarily Lindelöf. The assumption … Continue reading

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Young Researchers in Set Theory, March 2011

These are the slides of a talk I gave at the Young Researchers in Set Theory 2011 meeting (Königswinter, 21–25 March 2011). Talk Title: Around Jensen’s square principle Abstract: Jensen‘s square principle for a cardinal λ asserts the existence of a particular ladder … Continue reading

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Workshop on Set Theory and its Applications, February 2007

These are the slides of a talk given at the Workshop on Set Theory and its Applications workshop (Weizmann Institute, February 19, 2007). Talk Title: Nets of spaces having singular density Abstract: The weight of a topological space X is the … Continue reading

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