reserve a for set;

theorem
  for L being upper-bounded non empty Poset
  for F being Filter of L holds Top L in F
proof
  let L be upper-bounded non empty Poset;
  let F be Filter of L;
  set x = the Element of F;
  Top L >= x by YELLOW_0:45;
  hence thesis by WAYBEL_0:def 20;
end;
