
theorem Th8: :: 1.3.0.
  for T being TopStruct, A being Subset of T holds Fr A = Cl A \ Int A
proof
  let T be TopStruct, A be Subset of T;
  Fr A = Cl A /\ (Cl A`)`` by TOPS_1:def 2
    .= Cl A \ (Cl A`)` by SUBSET_1:13
    .= Cl A \ Int A by TOPS_1:def 1;
  hence thesis;
end;
