What ordered pair$($s$)$ would we have to include in the set f in order to

make it defined by the rule?

f $=\{(($aaab$,$ aaa$),($aaba$,$ aab$),($abaa$,$ aba$),($baaa$,$ baa$),($aabb$,$ aab$),($abab$,$ aba$),($abba$,$ abb$),$

$($baab$,$ baa$),($baba$,$ bab$),($bbaa$,$ bba$),($bbba$,$ bbb$),($bbab$,$ bba$),($babb$,$ bab$),($abbb$,$ abb$)$