deffunc H₁( set , Sequence) -> set = union (rng $2);
deffunc H₂( Ordinal, set ) -> set = new_set2 $2;
( ex x being object ex L0 being Sequence st
( x = last L0 & dom L0 = succ O & L0 . 0 = A & ( for C being Ordinal st succ C in succ O holds
L0 . (succ C) = H₂(C,L0 . C) ) & ( for C being Ordinal st C in succ O & C <> 0 & C is limit_ordinal holds
L0 . C = H₁(C,L0 | C) ) ) & ( for x1, x2 being set st ex L0 being Sequence st
( x1 = last L0 & dom L0 = succ O & L0 . 0 = A & ( for C being Ordinal st succ C in succ O holds
L0 . (succ C) = H₂(C,L0 . C) ) & ( for C being Ordinal st C in succ O & C <> 0 & C is limit_ordinal holds
L0 . C = H₁(C,L0 | C) ) ) & ex L0 being Sequence st
( x2 = last L0 & dom L0 = succ O & L0 . 0 = A & ( for C being Ordinal st succ C in succ O holds
L0 . (succ C) = H₂(C,L0 . C) ) & ( for C being Ordinal st C in succ O & C <> 0 & C is limit_ordinal holds
L0 . C = H₁(C,L0 | C) ) ) holds
x1 = x2 ) ) from ORDINAL2:sch 7();
hence ( ex b₁ being set ex L0 being Sequence st
( b₁ = last L0 & dom L0 = succ O & L0 . 0 = A & ( for C being Ordinal st succ C in succ O holds
L0 . (succ C) = new_set2 (L0 . C) ) & ( for C being Ordinal st C in succ O & C <> 0 & C is limit_ordinal holds
L0 . C = union (rng (L0 | C)) ) ) & ( for b₁, b₂ being set st ex L0 being Sequence st
( b₁ = last L0 & dom L0 = succ O & L0 . 0 = A & ( for C being Ordinal st succ C in succ O holds
L0 . (succ C) = new_set2 (L0 . C) ) & ( for C being Ordinal st C in succ O & C <> 0 & C is limit_ordinal holds
L0 . C = union (rng (L0 | C)) ) ) & ex L0 being Sequence st
( b₂ = last L0 & dom L0 = succ O & L0 . 0 = A & ( for C being Ordinal st succ C in succ O holds
L0 . (succ C) = new_set2 (L0 . C) ) & ( for C being Ordinal st C in succ O & C <> 0 & C is limit_ordinal holds
L0 . C = union (rng (L0 | C)) ) ) holds
b₁ = b₂ ) ) ; :: thesis: verum