TRS:
 {    fib(0()) -> 0(),
   fib(s(0())) -> s(0()),
  fib(s(s(x))) -> +(fib(s(x)), fib(x)),
     +(x, 0()) -> x,
    +(x, s(y)) -> s(+(x, y))}
 MPO:
  Prec:
   fib > +, 
   + > s
   empty
  Strict:
   {}
   Weak:
    {}
  Qed