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The given Problem was:
a a a -> a b b 
b a b -> a b a 
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A self-embedding rewrite structure for the given SRS is:
   a a a a b a --(6)-> a a a a b a (#98)
   OC+OC at 3
      OC: a a a a b a --(5)-> a a a b a b (#74)
          OC+OC at 2
             OC: a a a a b a --(4)-> a a b a b b (#27)
                 OC+OC at 3
                    OC: a a a a b --(3)-> a a b a a (#15)
                        OC+OC at 1
                           OC: a a a a b --(2)-> a b a b a (#5)
                               OC+OC at 2
                                  OC: a a a --(1)-> a b b (#1)
                                      Rule
                                  OC: b a b --(1)-> a b a (#2)
                                      Rule
                           OC: b a b --(1)-> a b a (#2)
                               Rule
                    OC: a a a --(1)-> a b b (#1)
                        Rule
             OC: b a b --(1)-> a b a (#2)
                 Rule
      OC: b a b --(1)-> a b a (#2)
          Rule
Hence, the SRS is non-terminating.