for D1, D2 being non empty set
for a1 being Element of D1
for a2 being Element of D2
for f1 being BinOp of D1
for f2 being BinOp of D2 holds
( ( a1 is_a_unity_wrt f1 & a2 is_a_unity_wrt f2 ) iff [a1,a2] is_a_unity_wrt |:f1,f2:| ) by Th24, Th25;