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 Th140:
  r ++ (F \+\ G) = (r++F) \+\ (r++G)
proof
  thus r ++ (F \+\ G) = (r++(F\G)) \/ (r++(G\F)) by Th41
    .= ((r++F)\(r++G)) \/ (r++(G\F)) by Th139
    .= (r++F) \+\ (r++G) by Th139;
end;
