scheme :: PCOMPS_2:sch 3
XXX{ F₁() -> non empty set , F₂() -> Subset-Family of F₁(), F₃( object , object ) -> Subset of F₁(), P₁[ object ], P₂[ 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() : ( P₂[c,V,n] & not c in union { (union (f . q)) where q is Nat : q <= n } ) } ) where V is Subset of F₁() : P₁[V] } ) )