Editing If and only if (section)

===Origin of iff and pronunciation===
Usage of the abbreviation "iff" first appeared in print in [[John L. Kelley]]'s 1955 book ''General Topology''.<ref>''General Topology,'' reissue {{ISBN|978-0-387-90125-1}}</ref> Its invention is often credited to [[Paul Halmos]], who wrote "I invented 'iff,' for  'if and only if'—but I could never believe I was really its first inventor."<ref name="Higham1998">{{cite book |author=Nicholas J. Higham |title=Handbook of writing for the mathematical sciences |url=https://books.google.com/books?id=9gQd2fJA7Y4C&pg=PA24 |year=1998 |publisher=SIAM |isbn=978-0-89871-420-3 |page=24 |edition=2nd}}</ref>

It is somewhat unclear how "iff" was meant to be pronounced. In current practice, the single 'word' "iff" is almost always read as the four words "if and only if". However, in the preface of ''General Topology'', Kelley suggests that it should be read differently: "In some cases where mathematical content requires 'if and only if' and [[euphony]] demands something less I use Halmos' 'iff{{'"}}. The authors of one discrete mathematics textbook suggest:<ref>{{cite book |title=Discrete Algorithmic Mathematics |last=Maurer |first=Stephen B. |last2=Ralston |first2=Anthony |publisher=CRC Press |year=2005 |isbn=1568811667 |edition=3rd |location=Boca Raton, Fla. |pages=60}}</ref> "Should you need to pronounce iff, really [[Consonant gemination|hang on to the 'ff']] so that people hear the difference from 'if{{'"}}, implying that "iff" could be pronounced as {{IPA|[ɪfː]}}.