 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 IMeet:   :: Lemma 3.4. (I /\)
  x "/\" x = x
  proof
    thus x "/\" x = x "/\" (x "\/" x) by ISum
      .= x by LATTICES:def 9;
  end;
