if and only if

/IH1 F AH0 N D OW0 N L IY0 IH0 F/
conjunction
  1. 1

    Is equivalent to; implies and is implied by; is true and false in the same cases as.

    โ€œA rectangle is a square if and only if all four of its sides have the same length.โ€

Source: https://en.wiktionary.org/wiki/if%20and%20only%20if