          
                   
      1      
      2     
      3    
              
       1      
       2       
      (3      
               
      1           
      2             
       3          
              
       1       
      2        
      3      
               
       1           
       2           
       3         
               
      1           

      2              
      3           
                  
      1          

      2             
      3          
              

     1               
     (2           
     3            
            
     1         
     2          
     3          

  
                