    0        
            
0         
        5  5        
     
               
     a    a  
              
       
  0   0          
 
2             
       
1                   
     
2                           
                  
3    0         
            
                
       
                         
         
              
   
                         
                     
         
  0     
 1         
             
ab=ba
             
            

            
    a=an.1(b  0)0     
           
    
a.a....a  a   a  n    n  
      
  
     a     n    
               
      
           0     
  
            
  
1              

2           
3                         
    
 
 0.025