reserve E, x, y, X for set;
reserve A, B, C for Subset of E^omega;
reserve a, a1, a2, b for Element of E^omega;
reserve i, k, l, m, n for Nat;

theorem Th61:
  A c= B* implies A+ c= B*
proof
  assume A c= B*;
  then A+ c= (B*)+ by Th58;
  hence thesis by Th60;
end;
