A3:
dom (f ^2) = dom f
by VALUED_1:11;

len f = n by CARD_1:def 7;

hence len (f ^2) = n by A3, FINSEQ_3:29; :: according to CARD_1:def 7 :: thesis: verum

len f = n by CARD_1:def 7;

hence len (f ^2) = n by A3, FINSEQ_3:29; :: according to CARD_1:def 7 :: thesis: verum