Definition talk:Closed under Mapping

Isn't $S \subseteq X$ required? --abcxyz (talk) 19:38, 6 October 2012 (UTC)


 * Is it possible to make a simpler version of this which does not need to use the language of families? Subsets of a power set for example? --prime mover (talk) 20:53, 6 October 2012 (UTC)