theorem :: SETWOP_2:19

for C, D being non empty set
for B being Element of Fin C
for F being BinOp of D
for f being Function of C,D st F is commutative & F is associative & F is having_a_unity & F is having_an_inverseOp holds
(the_inverseOp_wrt F) . (F $$ (B,f)) = F $$ (B,((the_inverseOp_wrt F) * f))