161 research outputs found

    Easton supported Jensen coding and projective measure without projective Baire

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    We prove that it is consistent relative to a Mahlo cardinal that all sets of reals definable from countable sequences of ordinals are Lebesgue measurable, but at the same time, there is a Ξ”31\Delta^1_3 set without the Baire property. To this end, we introduce a notion of stratified forcing and stratified extension and prove an iteration theorem for these classes of forcings. Moreover we introduce a variant of Shelah's amalgamation technique that preserves stratification. The complexity of the set which provides a counterexample to the Baire property is optimal.Comment: 142 page

    Embeddings into outer models

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    We explore the possibilities for elementary embeddings j:Mβ†’Nj : M \to N, where MM and NN are models of ZFC with the same ordinals, MβŠ†NM \subseteq N, and NN has access to large pieces of jj. We construct commuting systems of such maps between countable transitive models that are isomorphic to various canonical linear and partial orders, including the real line R\mathbb R

    Subcompact cardinals, squares, and stationary reflection

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    We generalise Jensen's result on the incompatibility of subcompactness with square. We show that alpha^+-subcompactness of some cardinal less than or equal to alpha precludes square_alpha, but also that square may be forced to hold everywhere where this obstruction is not present. The forcing also preserves other strong large cardinals. Similar results are also given for stationary reflection, with a corresponding strengthening of the large cardinal assumption involved. Finally, we refine the analysis by considering Schimmerling's hierarchy of weak squares, showing which cases are precluded by alpha^+-subcompactness, and again we demonstrate the optimality of our results by forcing the strongest possible squares under these restrictions to hold.Comment: 18 pages. Corrections and improvements from referee's report mad
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