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Non-Glimm–Effros equivalence relations at second projective level

Vladimir Kanovei — 1997

Fundamenta Mathematicae

A model is presented in which the Σ 2 1 equivalence relation xCy iff L[x]=L[y] of equiconstructibility of reals does not admit a reasonable form of the Glimm-Effros theorem. The model is a kind of iterated Sacks generic extension of the constructible model, but with an “ill“founded “length” of the iteration. In another model of this type, we get an example of a Π 2 1 non-Glimm-Effros equivalence relation on reals. As a more elementary application of the technique of “ill“founded Sacks iterations, we obtain...

Two dichotomy theorems on colourability of non-analytic graphs

Vladimir Kanovei — 1997

Fundamenta Mathematicae

We prove:  Theorem 1. Let κ be an uncountable cardinal. Every κ-Suslin graph G on reals satisfies one of the following two requirements: (I) G admits a κ-Borel colouring by ordinals below κ; (II) there exists a continuous homomorphism (in some cases an embedding) of a certain locally countable Borel graph G 0 into G.  Theorem 2. In the Solovay model, every OD graph G on reals satisfies one of the following two requirements: (I) G admits an OD colouring by countable ordinals; (II) as above.

On countable cofinality and decomposition of definable thin orderings

Vladimir KanoveiVassily Lyubetsky — 2016

Fundamenta Mathematicae

We prove that in some cases definable thin sets (including chains) of Borel partial orderings are necessarily countably cofinal. This includes the following cases: analytic thin sets, ROD thin sets in the Solovay model, and Σ¹₂ thin sets under the assumption that ω L [ x ] < ω for all reals x. We also prove that definable thin wellorderings admit partitions into definable chains in the Solovay model.

19th-century real analysis, forward and backward

Jacques BairPiotr BlaszczykPeter HeinigVladimir KanoveiMikhail Katz — 2019

Antiquitates Mathematicae

19th-century real analysis received a major impetus from Cauchy's work. Cauchy mentions variable quantities, limits, and infinitesimals, but the meaning he attached to these terms is not identical to their modern meaning. Some Cauchy historians work in a conceptual scheme dominated by an assumption of a teleological nature of the evolution of real analysis toward a preordained outcome. Thus, Gilain and Siegmund-Schultze assume that references to limite in Cauchy's work necessarily imply that Cauchy...

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