 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
   A, B, C is_a_triangle implies A, C, B is_a_triangle &
  B, A, C is_a_triangle & B, C, A is_a_triangle & C, A, B is_a_triangle &
  C, B, A is_a_triangle;
