scheme :: METRIC_3:sch 2
LambdaMCART1{ F₁() -> non empty set , F₂() -> non empty set , F₃() -> non empty set , F₄() -> non empty set , F₅( object , object , object , object , object , object ) -> Element of F₄() } :

ex f being Function of [:[:F₁(),F₂(),F₃():],[:F₁(),F₂(),F₃():]:],F₄() st
for x1, y1 being Element of F₁()
for x2, y2 being Element of F₂()
for x3, y3 being Element of F₃()
for x, y being Element of [:F₁(),F₂(),F₃():] st x = [x1,x2,x3] & y = [y1,y2,y3] holds
f . (x,y) = F₅(x1,y1,x2,y2,x3,y3)