reserve x for set,
  C for Ordinal,
  L0 for Sequence;

theorem Th14:
  for A being non empty set holds ConsecutiveSet2(A,0) = A
proof
  deffunc D(set,Sequence) = union rng $2;
  deffunc C(Ordinal,set) = new_set2 $2;
  let A be non empty set;
  deffunc F(Ordinal) = ConsecutiveSet2(A,$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 = A & (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 Def5;
  thus F(0) = A from ORDINAL2:sch 8(A1);
end;
