
theorem Th24:
  for T being TopStruct holds bool the carrier of T is basis of T
proof
  let T be TopStruct;
  reconsider P = bool the carrier of T as Subset-Family of T;
  reconsider P as Subset-Family of T;
  P is basis of T
  proof
    let p be Point of T;
    thus thesis by Th18;
  end;
  hence thesis;
end;
