(17c)                                     (18a)                                              
               (17b)                                                                                                                                                                                                    (18b)                                           (19a)               
  
 
 
 
 
 
 
 
 
 
 
 
 
                                                                                                                                                              (20)                                                                                                                                       
                  (19b)                                                 (19c)                                                                                                                                     (21a)                                                (21b)