reserve x, y for set,
  T for TopStruct,
  GX for TopSpace,
  P, Q, M, N for Subset of T,
  F, G for Subset-Family of T,
  W, Z for Subset-Family of GX,
  A for SubSpace of T;

theorem Th29:
  M /\ N is Subset of T|N
proof
  M /\ N c= N by XBOOLE_1:17;
  then M /\ N c= [#](T|N) by PRE_TOPC:def 5;
  hence thesis;
end;
