theorem Th37:
  the carrier of FixPoints f c= the carrier of L
proof
A1: the carrier of FixPoints f = {x where x is Element of L: x
  is_a_fixpoint_of f} by Th36;
  let x be object;
  assume x in the carrier of FixPoints f;
  then ex a st x = a & a is_a_fixpoint_of f by A1;
  hence thesis;
end;
