theorem Th50:
  Lang(w, {}(E^omega, E^omega)) = {w}
proof
  for x holds not(x <> w & x in Lang(w, {}(E^omega, E^omega))) by Th46,Th42;
  then for x be object holds x in Lang(w, {}(E^omega, E^omega)) iff x = w
  by Th47;
  hence thesis by TARSKI:def 1;
end;
