5 found
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  1. Dualization of the Van Douwen Diagram.Jacek Cichoń, Adam Krawczyk, Barbara Majcher-Iwanow & Bogdan Weglorz - 2000 - Journal of Symbolic Logic 65 (2):959-968.
    We make a more systematic study of the van Douwen diagram for cardinal coefficients related to combinatorial properties of partitions of natural numbers.
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    Gδ‐Pieces of Canonical Partitions of G‐Spaces.Barbara Majcher-Iwanow - 2005 - Mathematical Logic Quarterly 51 (5):450-461.
    Generalizing model companions from model theory we define companions of pieces of canonical partitions of Polish G-spaces. This unifies several constructions from logic. The central problem of the paper is the existence of companions which form a G-orbit which is a Gδ-set. We describe companions of some typical G-spaces.
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    Polish Group Actions, Nice Topologies, and Admissible Sets.Barbara Majcher-Iwanow - 2008 - Mathematical Logic Quarterly 54 (6):597-616.
    Let G be a closed subgroup of S∞ and X be a Polish G -space. To every x ∈ X we associate an admissible set Ax and show how questions about X which involve Baire category can be formalized in Ax.
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    Eventually Open Action.Barbara Majcher-Iwanow - 2012 - Mathematical Logic Quarterly 58 (1-2):95-104.
    We study a natural subclass of continuous actions of Polish groups on Polish spaces which we call eventually open actions. We prove that this property characterizes the actions endowed with a complete system of hereditarily countable invariant structures introduced by Hjorth as a generalization of Scott sentences.
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    Polish Group Actions and Effectivity.Barbara Majcher-Iwanow - 2012 - Archive for Mathematical Logic 51 (5-6):563-573.
    We extend a theorem of Barwise and Nadel describing the relationship between approximations of canonical Scott sentences and admissible sets to the case of orbit equivalence relations induced on an arbitrary Polish space by a Polish group action.
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