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 Th151:
  a ++ (A \+\ B) = (a++A) \+\ (a++B)
proof
  thus a ++ (A \+\ B) = (a++(A\B)) \/ (a++(B\A)) by Th48
    .= ((a++A)\(a++B)) \/ (a++(B\A)) by Th150
    .= (a++A) \+\ (a++B) by Th150;
end;
