 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 Th3716: :: Theorem 3.7. (1) <=> (6)
  (x "/\" y) "\/" x = x iff x "\/" y = y "\/" x
  proof
    hereby
      assume
A1:   (x "/\" y) "\/" x = x;
      x "/\" (y "\/" x) = x by A1,Th3712;
      hence x "\/" y = y "\/" x by Th3726;
    end;
    assume x "\/" y = y "\/" x; then
    x "/\" (y "\/" x) = x by LATTICES:def 9;
    hence thesis by Th3712;
  end;
