theorem Th27:
  for d be BiFunction of A,L for q being QuadrSeq of d holds
  ConsecutiveDelta(q,succ O) = new_bi_fun(BiFun(ConsecutiveDelta(q,O),
  ConsecutiveSet(A,O),L),Quadr(q,O))
proof
  deffunc D(Ordinal,Sequence) = union rng $2;
  let d be BiFunction of A,L;
  let q be QuadrSeq of d;
  deffunc C(Ordinal,set) = new_bi_fun(BiFun($2,ConsecutiveSet(A,$1),L),Quadr(q
  ,$1));
  deffunc F(Ordinal) = ConsecutiveDelta(q,$1);
A1: for O being Ordinal, It being object holds It = F(O) iff ex L0 being
Sequence st It = last L0 & dom L0 = succ O & L0.0 = d & (for C being Ordinal
st succ C in succ O holds L0.succ C = C(C,L0.C)) & for C being Ordinal st C in
  succ O & C <> 0 & C is limit_ordinal holds L0.C = D(C,L0|C) by Def16;
  for O holds F(succ O) = C(O,F(O)) from ORDINAL2:sch 9(A1);
  hence thesis;
end;
