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Universal ${ \aleph }_{2}$-Aronszajn trees - Dzamonja, Mirna (Auteur de la conférence) | CIRM H

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We report on a joint work in progress with Rahman Mohammadpour in which we study the problem of the possible existence of a universal tree under weak embeddings in the classes of $\aleph_{2}$-Aronszajn and wide $\aleph_{2}$-Aronszajn trees. This problem is more complex than previously thought, in particular it seems not to be resolved under ShFA $+$ CH using the technology of weakly Lipshitz trees. We show that under CH, for a given $\aleph_{2}$-Aronszajn tree $\mathrm{T}$ without a weak ascent path, there is an $\aleph_{2^{-\mathrm{C}\mathrm{C}}}$ countably closed forcing forcing which specialises $\mathrm{T}$ and adds an $\aleph_{2}$-Aronszajn tree which does not embed into T. One cannot however apply the ShFA to this forcing.[-]
We report on a joint work in progress with Rahman Mohammadpour in which we study the problem of the possible existence of a universal tree under weak embeddings in the classes of $\aleph_{2}$-Aronszajn and wide $\aleph_{2}$-Aronszajn trees. This problem is more complex than previously thought, in particular it seems not to be resolved under ShFA $+$ CH using the technology of weakly Lipshitz trees. We show that under CH, for a given $\a...[+]

03E05 ; 03E35 ; 03E50

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In 1971 Baumgartner showed it is consistent that any two $\aleph_1$-dense subsets of the real line are order isomorphic. This was important both for the methods of the proof and for consequences of the result. We introduce methods that lead to an analogous result for $\aleph_2$-dense sets.

Keywords : forcing - large cardinals - Baumgartner isomorphism - infinitary Ramsey principles - reflection principles

03E35 ; 03E05 ; 03E50 ; 03E55 ; 03E57

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A journey guided by the stars - Lietz, Andreas (Auteur de la conférence) | CIRM H

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We show that starting from an inaccessible limit of supercompact cardinals, there is a staionary set preserving forcing so that the Nonstationary Ideal is dense in the generic extension. This answers positively a question of Woodin.

03E35 ; 03E50 ; 03E55

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