 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;

theorem   :: Theorem 3.9. (1) <=> (2)
  x "/\" y = y "/\" x iff x "/\" y [= x by LATTICES:def 8,Th3715;
