 reserve A, B, C, A1, B1, C1, A2, B2, C2, C3 for Point of TOP-REAL 2,
  lambda, mu, nu, alpha, beta, gamma for Real,
  X, Y, Z for Subset of TOP-REAL 2;

theorem
  Th3: (- A) `1 = - A `1 & (- A) `2 = - A `2
proof
  - A = |[- A `1, - A `2]| by EUCLID:59;
  hence thesis by EUCLID:52;
end;
