for D being non empty set
for d1, d2 being Element of D
for F being BinOp of D
for i being Nat st F is commutative & F is associative & F is having_a_unity holds
F "**" (i |-> (F . (d1,d2))) = F . ((F "**" (i |-> d1)),(F "**" (i |-> d2)))