reserve T for TopSpace,
  A, B for Subset of T;

theorem :: Remark 1
  for T being TopSpace holds [#]T is regular_open & [#]T is regular_closed
proof
  let T be TopSpace;
A1: Int [#]T = [#]T by TOPS_1:15;
  Cl [#]T = [#]T by TOPS_1:2;
  hence thesis by A1,TOPS_1:def 7,def 8;
end;
