.0)  (0.0, .0) (0.0,0.0)  (0.0,0.0)  (0.0, .0)[$0$]{} (0.0,.0)[$a$]{}  (0.0,0.0)[$0$]{}  (.0,.0)[${\bf L}_0$  :]{}  (0.0, .0)[(0,0)[0.0]{}]{} (0.0,0)     $\to$      0      $a$      0   --------- ------ -------- -----       0       0       0       0      $a$      0       0      $a$       0       0      $a$      0  (0.0, .0) (0.0,0.0)  (0.0, 0.0)  (0.0, .0)[$0$]{} (0.0,.0)[$a$]{}  (0.0,0.0)[$0$]{}  (0.0,.0)[${\bf L}_0$  :]{} (0.0, .0)[(0,0)[0.0]{}]{}  (0.0,0)     $\to$      0      $a$      0   --------- ------ -------- -----       0       0      $a$      0      $a$      0       0      $a$       0       0      $a$      0  \  (0,