NO

Problem:
 f(tt(),x) -> f(isList(x),x)
 isList(Cons(x,xs())) -> isList(xs())
 isList(nil()) -> tt()

Proof:
 Unfolding Processor:
  loop length: 2
  terms:
   f(isList(nil()),nil())
   f(tt(),nil())
  context: []
  substitution:
   
  Qed