Author Archives: Assaf Rinot

Reflection on the coloring and chromatic numbers

Joint work with Chris Lambie-Hanson. Abstract.  We prove that reflection of the coloring number of graphs is consistent with non-reflection of the chromatic number.  Moreover, it is proved that incompactness for the chromatic number of graphs (with arbitrarily large gaps) … Continue reading

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Set Theory and its Applications in Topology, September 2016

I gave an invited talk at the Set Theory and its Applications in Topology meeting, Oaxaca, September 11-16, 2016. The talk was on the 2-Souslin problem. If you are interested in seeing the effect of a jet lag, the video is … Continue reading

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Strong failures of higher analogs of Hindman’s Theorem

Joint work with David J. Fernández Bretón. Abstract.  We show that various analogs of Hindman’s Theorem fail in a strong sense when one attempts to obtain uncountable monochromatic sets: Theorem 1. There exists a colouring c:RQ, such that … 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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Prikry forcing may add a Souslin tree

A celebrated theorem of Shelah states that adding a Cohen real introduces a Souslin tree. Are there any other examples of notions of forcing that add a κ-Souslin tree? and why is this of interest? My motivation comes from a … Continue reading

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The reflection principle R2

A few years ago, in this paper, I introduced the following reflection principle: Definition. R2(θ,κ) asserts that for every function f:E<κθκ, there exists some j<κ for which the following set is nonstationary: Aj:={δEκθf1[j]δ is nonstationary}. I wrote there … 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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Higher Souslin trees and the GCH, revisited

Abstract.  It is proved that for every uncountable cardinal λ, GCH+◻(λ+) entails the existence of a cf(λ)-complete λ+-Souslin tree. In particular, if GCH holds and there are no 2-Souslin trees, then 2 is weakly compact in Godel’s constructible universe, improving … Continue reading

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Prolific Souslin trees

In a paper from 1971, Erdos and Hajnal asked whether (assuming CH) every coloring witnessing 1[1]32 has a rainbow triangle. The negative solution was given in a 1975 paper by Shelah, and the proof and relevant definitions may be found … Continue reading

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A microscopic approach to Souslin-tree constructions. Part I

Joint work with Ari Meir Brodsky. Abstract.  We propose a parameterized proxy principle from which κ-Souslin trees with various additional features can be constructed, regardless of the identity of κ. We then introduce the microscopic approach, which is a simple … Continue reading

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