 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 3.8. 1) <=> 3)
  x "\/" y = y "\/" x iff ex z st x [= z & y [= z by Th3823,LemX3,DefB2;
