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;
