scheme :: AOFA_A00:sch 3
Sch2{ F1() -> non empty set , F2( set , set ) -> Element of F1() } :
ex f being non empty homogeneous quasi_total 2 -ary PartFunc of (F1() *),F1() st
for a, b being Element of F1() holds f . <*a,b*> = F2(a,b)