theorem Th39:
  B is constant & the_value_of B = A implies for n holds (
  superior_setsequence B).n = A
proof
  assume
A1: B is constant & the_value_of B = A;
  let n;
  (superior_setsequence(B)).n = union {B.k : n <= k} by Def3;
  hence thesis by A1,Th13;
end;
