The effective Borel hierarchy
نویسندگان
چکیده
منابع مشابه
The hierarchy of ω 1 - Borel sets 1 The hierarchy of ω 1 - Borel sets Arnold
We consider the ω1-Borel subsets of the reals in models of ZFC. This is the smallest family of sets containing the open subsets of the 2 and closed under ω1 intersections and ω1 unions. We show that Martin’s Axiom implies that the hierarchy of ω1-Borel sets has length ω2. We prove that in the Cohen real model the length of this hierarchy is at least ω1 but no more than ω1 + 1. Some authors have...
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ژورنال
عنوان ژورنال: Fundamenta Mathematicae
سال: 2007
ISSN: 0016-2736,1730-6329
DOI: 10.4064/fm195-3-4