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 Th27:
  {f,g}"" = {f",g"}
proof
  thus {f,g}"" = ({f}\/{g})"" by ENUMSET1:1
    .= ({f}"") \/ ({g}"") by Th23
    .= {f"} \/ ({g}"") by Th26
    .= ({f"}) \/ {g"} by Th26
    .= {f",g"} by ENUMSET1:1;
end;
