Category Archives: Squares and Diamonds

A cofinality-preserving small forcing may introduce a special Aronszajn tree

Extended Abstract: Shelah proved that Cohen forcing introduces a Souslin tree; Jensen proved that a c.c.c. forcing may consistently add a Kurepa tree; Todorcevic proved that a Knaster poset may already force the Kurepa hypothesis; Irrgang introduced a c.c.c. notion … Continue reading

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The failure of diamond on a reflecting stationary set

Joint work with Moti Gitik. Abstract: It is shown that the failure of S, for a subset Sω+1 that reflects stationarily often, is consistent with GCH and APω, relatively to the existence of a supercompact cardinal. This should be comapred with … Continue reading

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A relative of the approachability ideal, diamond and non-saturation

Abstract: Let λ denote a singular cardinal. Zeman, improving a previous result of Shelah, proved that ◻λ together with 2λ=λ+ implies S for every Sλ+ that reflects stationarily often. In this paper, for a subset Sλ+, a normal subideal of … Continue reading

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On guessing generalized clubs at the successors of regulars

Abstract: Konig, Larson and Yoshinobu initiated the study of principles for guessing generalized clubs, and introduced a construction of an higher Souslin tree from the strong guessing principle. Complementary to the author’s work on the validity of diamond and non-saturation … Continue reading

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The Ostaszewski square, and homogeneous Souslin trees

Abstract: Assume GCH and let λ denote an uncountable cardinal. We prove that if ◻λ holds, then this may be  witnessed by a coherent sequence Cαα<λ+ with the following remarkable guessing property: For every sequence Aii<λContinue reading

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