reserve T for non empty TopSpace,
  X,Z for Subset of T;
reserve x,y for Element of OpenClosedSet(T);
reserve x,y,X for set;
reserve BL for non trivial B_Lattice,
  a,b,c,p,q for Element of BL,
  UF,F,F0,F1,F2 for Filter of BL;

theorem Th16:
  for a holds { F :F is being_ultrafilter & a in F} c= ultraset BL
proof
  let a;
  let x be object;
  assume x in { F :F is being_ultrafilter & a in F};
  then ex UF st ( UF = x)&( UF is being_ultrafilter)&( a in UF);
  hence thesis;
end;
