reserve TS for 1-sorted,
  K, Q for Subset of TS;
reserve TS for TopSpace,
  GX for TopStruct,
  x for set,
  P, Q for Subset of TS,
  K , L for Subset of TS,
  R, S for Subset of GX,
  T, W for Subset of GX;

theorem Th16:
  Int T c= T
proof
  let x be object;
  assume
A1: x in Int T;
  then reconsider x99= x as Point of GX;
  T` c= Cl T` by PRE_TOPC:18;
  then not x99 in T` by A1,XBOOLE_0:def 5;
  hence thesis by A1,XBOOLE_0:def 5;
end;
