PROCESSED              PROGRAM STRING
                       ((a,a))
(                       (a,a))
((                       a,a))
((a                       ,a))
((S                       ,a))
((S,                       a))
((S,a                       ))
((S,S                       ))
((S,Se                      ))
((S,SL'                     ))
((S,L                       ))
((SL'                       ))
((L                         ))
((L)                         )
(S                           )
(Se                          )
(SL'                         )
(L                           )
(L)                          .
S                            .