Editing If and only if (section)

==More general usage==
''Iff'' is used outside the field of logic as well. Wherever logic is applied, especially in [[mathematics|mathematical]] discussions, it has the same meaning as above: it is an abbreviation for ''if and only if'', indicating that one statement is both [[Necessary and sufficient conditions|necessary and sufficient]] for the other. This is an example of [[mathematical jargon]] (although, as noted above, ''if'' is more often used than ''iff'' in statements of definition).

The elements of ''X'' are ''all and only'' the elements of ''Y'' means: "For any ''z'' in the [[domain of discourse]], ''z'' is in ''X'' if and only if ''z'' is in ''Y''."