reserve T for TopStruct;
reserve GX for TopSpace;

theorem
  for A, B being Subset of T holds Cl (A /\ B) c= (Cl A) /\ Cl B
proof
  let A,B be Subset of T;
  Cl(A /\ B) c= Cl A & Cl(A /\ B) c= Cl B by Th19,XBOOLE_1:17;
  hence thesis by XBOOLE_1:19;
end;
