theorem
  for P, Q st Q c= P* holds Q* c= P*
proof
  let P, Q;
  assume A1: Q c= P*;
  let a;
  assume a in Q*;
  then consider n such that A2: a in Q^^n by Th5;
  Q^^n c= P* by Th14, A1;
  hence thesis by A2;
end;
