theorem Th56:
  lim_filter(s,Frechet_Filter([:NAT,NAT:])) c=
    lim_filter(s,<. all-square-uparrow.))
  proof
    <. all-square-uparrow .) = <. Frechet_Filter(NAT),Frechet_Filter(NAT).)
      by Th34,CARDFIL2:19,Th35;
    hence thesis by Th37,Th39,Th40;
  end;
