reserve T for TopStruct;
reserve GX for TopSpace;

theorem
  for T being 1-sorted, P being Subset of T holds P \/ P` = [#]T
proof
  let T be 1-sorted, P be Subset of T;
  P \/ P` = [#] the carrier of T by SUBSET_1:10
    .= the carrier of T;
  hence thesis;
end;
