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 Th36:
  --(A"") = (--A)""
proof
  let a;
A1: (-a)" = -a" by XCMPLX_1:222;
  hereby
    assume a in --A"";
    then -a in A"" by Th12;
    then (-a)" in A by Th29;
    then a" in --A by A1,Th12;
    hence a in (--A)"" by Th29;
  end;
  assume a in (--A)"";
  then a" in --A by Th29;
  then -a" in A by Th12;
  then -a in A"" by A1,Th29;
  hence thesis by Th12;
end;
