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 Th234:
  (A++B)///a = A///a ++ B///a
proof
  thus (A++B)///a = a"**(A++B) by Th37
    .= a"**A++a"**B by Th208
    .= A///a++a"**B by Th37
    .= A///a ++ B///a by Th37;
end;
