MAYBE
MAYBE
TRS:
 {
     a__f(X1, X2, X3) -> f(X1, X2, X3),
      a__f(a(), X, X) -> a__f(X, a__b(), b()),
               a__b() -> b(),
               a__b() -> a(),
            mark(b()) -> a__b(),
            mark(a()) -> a(),
  mark(f(X1, X2, X3)) -> a__f(X1, mark(X2), X3)
 }
 DUP: We consider a non-duplicating system.
  Trs:
   {
       a__f(X1, X2, X3) -> f(X1, X2, X3),
        a__f(a(), X, X) -> a__f(X, a__b(), b()),
                 a__b() -> b(),
                 a__b() -> a(),
              mark(b()) -> a__b(),
              mark(a()) -> a(),
    mark(f(X1, X2, X3)) -> a__f(X1, mark(X2), X3)
   }
  Fail