TRS:
 {  a__f(b(), X, c()) -> a__f(X, a__c(), X),
               a__c() -> b(),
  mark(f(X1, X2, X3)) -> a__f(X1, mark(X2), X3),
            mark(c()) -> a__c(),
            mark(b()) -> b(),
     a__f(X1, X2, X3) -> f(X1, X2, X3),
               a__c() -> c()}
 Fail