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 Th26:
  A |^ 2 = A ^^ A
proof
  thus A |^ 2 = A |^ (1 + 1) .= (A |^ 1) ^^ A by Th23
    .= A ^^ A by Th25;
end;
