scheme :: BINOP_1:sch 2
Lambda2{ F₁() -> set , F₂() -> set , F₃() -> set , F₄( object , object ) -> object } :

ex f being Function of [:F₁(),F₂():],F₃() st
for x, y being object st x in F₁() & y in F₂() holds
f . (x,y) = F₄(x,y)

provided

A1: for x, y being object st x in F₁() & y in F₂() holds
F₄(x,y) in F₃()