reserve E, x, y, X for set;
reserve A, B, C, D for Subset of E^omega;
reserve a, a1, a2, b, c, c1, c2, d, ab, bc for Element of E^omega;
reserve e for Element of E;
reserve i, j, k, l, n, n1, n2, m for Nat;

theorem Th61:
  A c= B implies A* c= B*
proof
  assume
A1: A c= B;
  B c= B* by Th43;
  then A c= B* by A1;
  hence thesis by Th60;
end;
