Wikipedia:Reference desk/Archives/Mathematics/2018 May 29

= May 29 =

Is the proposition $$\exists x\, ((\emptyset \in x) \land (x \in x))$$ decidable in ZF ?
ZF, including the Axiom of Regularity. HOTmag (talk) 18:56, 29 May 2018 (UTC)
 * Yes, the axiom of foundation (which some people call "regularity") implies that no set is an element of itself. --Trovatore (talk) 21:20, 29 May 2018 (UTC)
 * Thanx. BTW, not only "some people" (as you call them), but also our article Axiom of regularity. HOTmag (talk) 21:48, 29 May 2018 (UTC)
 * Unfortunately. --Trovatore (talk) 22:43, 29 May 2018 (UTC)
 * It seems like you dislike this name, and I wonder why... HOTmag (talk) 22:46, 29 May 2018 (UTC)
 * Oh, I could come up with reasons, I suppose, but it boils down to the fact that "foundation" is the more usual name in my experience, which of course is influenced by the particular set-theoretic subculture I worked in. --Trovatore (talk) 22:48, 29 May 2018 (UTC)