MAYBE
TRS:
 {   a__f(X1, X2, X3) -> f(X1, X2, X3),
    a__f(a(), b(), X) -> a__f(mark(X), X, mark(X)),
            mark(a()) -> a(),
            mark(b()) -> b(),
  mark(f(X1, X2, X3)) -> a__f(mark(X1), X2, mark(X3)),
            mark(c()) -> a__c(),
               a__c() -> a(),
               a__c() -> b(),
               a__c() -> c()}
 DP:
  Strict:
   {  a__f#(a(), b(), X) -> a__f#(mark(X), X, mark(X)),
      a__f#(a(), b(), X) -> mark#(X),
    mark#(f(X1, X2, X3)) -> a__f#(mark(X1), X2, mark(X3)),
    mark#(f(X1, X2, X3)) -> mark#(X1),
    mark#(f(X1, X2, X3)) -> mark#(X3),
              mark#(c()) -> a__c#()}
  Weak:
  {   a__f(X1, X2, X3) -> f(X1, X2, X3),
     a__f(a(), b(), X) -> a__f(mark(X), X, mark(X)),
             mark(a()) -> a(),
             mark(b()) -> b(),
   mark(f(X1, X2, X3)) -> a__f(mark(X1), X2, mark(X3)),
             mark(c()) -> a__c(),
                a__c() -> a(),
                a__c() -> b(),
                a__c() -> c()}
  EDG:
   {(mark#(f(X1, X2, X3)) -> a__f#(mark(X1), X2, mark(X3)), a__f#(a(), b(), X) -> mark#(X))
    (mark#(f(X1, X2, X3)) -> a__f#(mark(X1), X2, mark(X3)), a__f#(a(), b(), X) -> a__f#(mark(X), X, mark(X)))
    (mark#(f(X1, X2, X3)) -> mark#(X1), mark#(c()) -> a__c#())
    (mark#(f(X1, X2, X3)) -> mark#(X1), mark#(f(X1, X2, X3)) -> mark#(X3))
    (mark#(f(X1, X2, X3)) -> mark#(X1), mark#(f(X1, X2, X3)) -> mark#(X1))
    (mark#(f(X1, X2, X3)) -> mark#(X1), mark#(f(X1, X2, X3)) -> a__f#(mark(X1), X2, mark(X3)))
    (mark#(f(X1, X2, X3)) -> mark#(X3), mark#(f(X1, X2, X3)) -> a__f#(mark(X1), X2, mark(X3)))
    (mark#(f(X1, X2, X3)) -> mark#(X3), mark#(f(X1, X2, X3)) -> mark#(X1))
    (mark#(f(X1, X2, X3)) -> mark#(X3), mark#(f(X1, X2, X3)) -> mark#(X3))
    (mark#(f(X1, X2, X3)) -> mark#(X3), mark#(c()) -> a__c#())
    (a__f#(a(), b(), X) -> mark#(X), mark#(f(X1, X2, X3)) -> a__f#(mark(X1), X2, mark(X3)))
    (a__f#(a(), b(), X) -> mark#(X), mark#(f(X1, X2, X3)) -> mark#(X1))
    (a__f#(a(), b(), X) -> mark#(X), mark#(f(X1, X2, X3)) -> mark#(X3))
    (a__f#(a(), b(), X) -> mark#(X), mark#(c()) -> a__c#())
    (a__f#(a(), b(), X) -> a__f#(mark(X), X, mark(X)), a__f#(a(), b(), X) -> a__f#(mark(X), X, mark(X)))
    (a__f#(a(), b(), X) -> a__f#(mark(X), X, mark(X)), a__f#(a(), b(), X) -> mark#(X))}
   SCCS:
    Scc:
     {  a__f#(a(), b(), X) -> a__f#(mark(X), X, mark(X)),
        a__f#(a(), b(), X) -> mark#(X),
      mark#(f(X1, X2, X3)) -> a__f#(mark(X1), X2, mark(X3)),
      mark#(f(X1, X2, X3)) -> mark#(X1),
      mark#(f(X1, X2, X3)) -> mark#(X3)}
    SCC:
     Strict:
      {  a__f#(a(), b(), X) -> a__f#(mark(X), X, mark(X)),
         a__f#(a(), b(), X) -> mark#(X),
       mark#(f(X1, X2, X3)) -> a__f#(mark(X1), X2, mark(X3)),
       mark#(f(X1, X2, X3)) -> mark#(X1),
       mark#(f(X1, X2, X3)) -> mark#(X3)}
     Weak:
     {   a__f(X1, X2, X3) -> f(X1, X2, X3),
        a__f(a(), b(), X) -> a__f(mark(X), X, mark(X)),
                mark(a()) -> a(),
                mark(b()) -> b(),
      mark(f(X1, X2, X3)) -> a__f(mark(X1), X2, mark(X3)),
                mark(c()) -> a__c(),
                   a__c() -> a(),
                   a__c() -> b(),
                   a__c() -> c()}
     Fail