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The given Problem was:
a l -> l a 
r a -> a r 
b l -> b a r 
r b -> l b 
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A self-embedding rewrite structure for the given SRS is:
   b (a)^k lb --> b (a)^k+1 lb  (#9734)
   pattern overlapped by closure at r0
      RP: b (a)^k l --> b (a)^k+1 r  (#7233)
          pattern overlapped by pattern
             RP: b (a)^k l --> bar (a)^k  (#130)
                 pattern overlapped by closure at l-1
                    RP: (a)^k l --> l (a)^k  (#2)
                        self-overlapping Closure at -1
                           OC: a l --(1)-> l a (#1)
                               Rule
                    OC: b l --(1)-> b a r (#3)
                        Rule
             RP: r (a)^k --> (a)^k r  (#3)
                 self-overlapping Closure at 1
                    OC: r a --(1)-> a r (#2)
                        Rule
      OC: r b --(1)-> l b (#4)
          Rule
Hence, the SRS is non-terminating.