reserve X for non empty set;

theorem
  for FMT being non empty FMT_Space_Str holds ex S being RelStr st
  for x being Element of FMT holds U_FMT x is Subset of S
  proof
    let FMT be non empty FMT_Space_Str;
    set S=BoolePoset(the carrier of FMT);
    take S;
    thus thesis by WAYBEL_7:2;
  end;
