N. 3   N. -2
   
    X. 
   
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                             +---------------  +----------------
                            
                                               
    ----------                   +--------------     +----------------
                                          -
                                                
                                                    
    ----+-----+---------+----------+--+--+--+-----+-----+----------------
      1   2      3         4     5 6 7  8    9    10     11
    ----+-----+---------+----------+--+--+--+-----+-----+------+---------
    ___________________________________________________________
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                       ..                          
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
                                                      
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             4.