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On hereditarily small sets in ZF
Authors:M Randall Holmes
Institution:Department of Mathematics, Boise State University, 1910 University Drive, , Boise, ID, 83725 United States of America
Abstract:We show in urn:x-wiley:09425616:malq201300089:equation:malq201300089-math-0003 (the usual set theory without Choice) that for any set X, the collection of sets Y such that each element of the transitive closure of urn:x-wiley:09425616:malq201300089:equation:malq201300089-math-0004 is strictly smaller in size than X (the collection of sets hereditarily smaller than X) is a set. This result has been shown by Jech in the case urn:x-wiley:09425616:malq201300089:equation:malq201300089-math-0005 (where the collection under consideration is the set of hereditarily countable sets).
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