scheme :: PCOMPS_2:sch 2
XXX1{ F₁() -> non empty set , F₂() -> Subset-Family of F₁(), F₃( object , object ) -> Subset of F₁(), P₁[ object ], P₂[ object , object , object , object ] } :

ex f being sequence of (bool (bool F₁())) st
( f . 0 = F₂() & ( for n being Nat holds f . (n + 1) = { (union { F₃(c,n) where c is Element of F₁() : for fq being Subset-Family of F₁()
for q being Nat st q <= n & fq = f . q holds
P₂[c,V,n,fq] } ) where V is Subset of F₁() : P₁[V] } ) )