reserve w, w1, w2 for Element of ExtREAL;
reserve c, c1, c2 for Complex;
reserve A, B, C, D for complex-membered set;
reserve F, G, H, I for ext-real-membered set;
reserve a, b, s, t, z for Complex;
reserve f, g, h, i, j for ExtReal;
reserve r for Real;
reserve e for set;

theorem Th66:
  a in A & b in B implies a-b in A--B
proof
  A--B = {c1-c2: c1 in A & c2 in B} by Th65;
  hence thesis;
end;
