scheme :: PRVECT_4:sch 1
FuncEx3A{ F₁() -> set , F₂() -> set , F₃() -> set , F₄() -> set , P₁[ object , object , object , object ] } :

ex f being Function of [:F₁(),F₂(),F₃():],F₄() st
for x, y, w being object st x in F₁() & y in F₂() & w in F₃() holds
P₁[x,y,w,f . (x,y,w)]

provided

A1: for x, y, w being object st x in F₁() & y in F₂() & w in F₃() holds
ex z being object st
( z in F₄() & P₁[x,y,w,z] )