preconditions<                                                                                                                                              
                                                                         note right                                                                                                                                                  
                                                                                                                                                                                                                                     
                                                                         All Of:                                                                                                                                                     
                                                                         1.                                prec 1                                                                                                                    
                                                                         2.                                prec 2                                                                                                                    
                                                                         end note                                                                                                                                                    
                                                                                                                                                                                                                                     
                                                                                                                                                                                                                                     
                                                                         :do A                                                                                                                                                       
                                                                                                                                                                                                                                     
                                                                                                                                                                                                                                     
                                                                                                                                                                                                                                     
                                                              yes                                         success?                                                                                                                 no
                                                                                                                                                                                                                                     
                                                                                                                                                                                                                                     
                                                                                                                                               no                                                                                    
                                     A is OK?                                                                                                                                                                  do C                  
                                                                                                                                                                                                                                     
                                                                                        yes                                                                                                                                          
                                                                                                                                                                                                                                     
                                                                                                                                                                                                                                     
                                                      do B