do 1                                                                                                                                                                                                                       
                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
                                                                                                                                              yes                                                                                                                                                                           no                                                                                                                                        
                                                                                                                                              CASE 1                                                                                                                                                                        CASE 3                                                                                                                                    
                                                                                                                                              CASE 2                                                                                                                                                                        CASE 4                                                                                                                                    
                                                                                                                                                                                                                                 success                                                                                                                                                                                                                              
                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
                                                                                                       do b                                                                                                                                                                                                                                                                    do c                                                                                   
                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
          yes                                                                                                                                                                          no                                                                                         yes                                                                                                                                                                           no    
          CASE 1                                                                                                                                                                       CASE 2                                                                                     CASE 3                                                                                                                                                                        CASE 4
                                                                                            success                                                                                                                                                                                                                                                                  success