 reserve L for AD_Lattice;
 reserve x,y,z for Element of L;
 reserve L for GAD_Lattice;
 reserve x,y,z for Element of L;
reserve L for with_zero GAD_Lattice,
        x,y for Element of L;

theorem   :: Lemma 3.17.
  x "/\" y = bottom L implies x "\/" y = y "\/" x
  proof
    assume x "/\" y = bottom L; then
    (y "/\" x) "\/" y = y by Th3751,Lem316;
    hence thesis by Th3716;
  end;
