MAYBE

We are left with following problem, upon which TcT provides the
certificate MAYBE.

Strict Trs:
  { fst(0(), Z) -> nil()
  , fst(s(X), cons(Y, Z)) -> cons(Y, fst(X, Z))
  , from(X) -> cons(X, from(s(X)))
  , add(0(), X) -> X
  , add(s(X), Y) -> s(add(X, Y))
  , len(nil()) -> 0()
  , len(cons(X, Z)) -> s(len(Z)) }
Obligation:
  innermost runtime complexity
Answer:
  MAYBE

The input cannot be shown compatible

Arrrr..