TRS:
 {    a__c() -> a__f(g(c())),
  a__f(g(X)) -> g(X),
   mark(c()) -> a__c(),
  mark(f(X)) -> a__f(X),
  mark(g(X)) -> g(X),
      a__c() -> c(),
     a__f(X) -> f(X)}
 Fail