"iff" was intended as "if and only if". while exact use of abbreviations isn't clear cut, I assumed this was a typo & it's not used anywhere else in source/, expand to "only if" (suggested by Sybren).
"iff" was intended as "if and only if". while exact use of abbreviations isn't clear cut, I assumed this was a typo & it's not used anywhere else in source/, expand to "only if" (suggested by Sybren).