reserve L for Lattice,
  p,q,r for Element of L,
  p9,q9,r9 for Element of L.:,
  x, y for set;
reserve I,J for Ideal of L,
  F for Filter of L;
reserve D for non empty Subset of L,
  D9 for non empty Subset of L.:;
reserve D1,D2 for non empty Subset of L,
  D19,D29 for non empty Subset of L.:;
reserve B for B_Lattice,
  IB,JB for Ideal of B,
  a,b for Element of B;
reserve a9 for Element of (B qua Lattice).:;
reserve P for non empty ClosedSubset of L,
  o1,o2 for BinOp of P;

theorem
  [#p,p#] = {p}
proof
  let q;
  hereby
    assume q in [#p,p#];
    then p [= q & q [= p by Th62;
    then q = p by LATTICES:8;
    hence q in {p} by TARSKI:def 1;
  end;
  p in [#p,p#] by Th62;
  hence thesis by TARSKI:def 1;
end;
