most recent 30 from http://mathoverflow.net 2013-05-19T22:33:49Z http://mathoverflow.net/feeds/question/30028 http://www.creativecommons.org/licenses/by-nc/2.5/rdf http://mathoverflow.net/questions/30028/about-tarskis-axioms-a-and-a-5-the-case-of-the-axiom-of-union Gérard Lang 2010-06-30T09:40:23Z 2010-06-30T09:40:23Z

<p>5-On page 85 of his article, Tarski also asserts that the axiom of Union can be derived from the axiom variant C obtained by taking C1=A1, C2=A'2, C3=A'3 and C4=A4. QUESTION 5 (i) Does anyone know aboutan explicit proof of this assertion ? (ii) In view of the fact that this variant C could be proved equivalent to axiom A, so that the axiom of union could be proved from "ZFC + Axiom A", would it be possible to also delete the axiom of Union, so that "Extensionality, Replacement, axiom A and Regularity" be a theory provably equivalent to "ZFC + Axiom A ?" Gérard LANG </p>