for D being non empty set
for d, d1, d2 being Element of D
for F being BinOp of D st F is having_a_unity & F is associative & F is having_an_inverseOp & ( F . (d,d1) = F . (d,d2) or F . (d1,d) = F . (d2,d) ) holds
d1 = d2