no                                 x?                                  yes                                    
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                       A                                                                                                                                      B
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                    yes                                                                                                        
                                 y?                                                                                                                                            
                                                                                                                                                                               
                                                no                                                                                                                             
                                                                                                                                                                               
                                                                                                                                                                               
                                       C                                                                                                                                       
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                          D                                                                    
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                                                                                               
                                                                                                          E