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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...

Nonmeasurable algebraic sums of sets of reals

Marcin Kysiak (2005)

Colloquium Mathematicae

We present a theorem which generalizes some known theorems on the existence of nonmeasurable (in various senses) sets of the form X+Y. Some additional related questions concerning measure, category and the algebra of Borel sets are also studied.

Nonnormality points of βX∖X

William Fleissner, Lynne Yengulalp (2011)

Fundamenta Mathematicae

Let X be a crowded metric space of weight κ that is either κ ω -like or locally compact. Let y ∈ βX∖X and assume GCH. Then a space of nonuniform ultrafilters embeds as a closed subspace of (βX∖X)∖y with y as the unique limit point. If, in addition, y is a regular z-ultrafilter, then the space of nonuniform ultrafilters is not normal, and hence (βX∖X)∖y is not normal.

Nonparametric recursive aggregation process

Elena Tsiporkova, Veselka Boeva (2004)

Kybernetika

In this work we introduce a nonparametric recursive aggregation process called Multilayer Aggregation (MLA). The name refers to the fact that at each step the results from the previous one are aggregated and thus, before the final result is derived, the initial values are subjected to several layers of aggregation. Most of the conventional aggregation operators, as for instance weighted mean, combine numerical values according to a vector of weights (parameters). Alternatively, the MLA operators...

Non-perfect rings and a theorem of Eklof and Shelah

Jan Trlifaj (1991)

Commentationes Mathematicae Universitatis Carolinae

We prove a stronger form, A + , of a consistency result, A , due to Eklof and Shelah. A + concerns extension properties of modules over non-left perfect rings. We also show (in ZFC) that A does not hold for left perfect rings.

Nonreflecting stationary subsets of P κ λ

Yoshihiro Abe (2000)

Fundamenta Mathematicae

We explore the possibility of forcing nonreflecting stationary sets of P κ λ . We also present a P κ λ generalization of Kanamori’s weakly normal filters, which induces stationary reflection.

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