MAYBE

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

Strict Trs:
  { fst(X1, X2) -> n__fst(X1, X2)
  , fst(0(), Z) -> nil()
  , fst(s(X), cons(Y, Z)) ->
    cons(Y, n__fst(activate(X), activate(Z)))
  , activate(X) -> X
  , activate(n__fst(X1, X2)) -> fst(X1, X2)
  , activate(n__from(X)) -> from(X)
  , activate(n__add(X1, X2)) -> add(X1, X2)
  , activate(n__len(X)) -> len(X)
  , from(X) -> cons(X, n__from(s(X)))
  , from(X) -> n__from(X)
  , add(X1, X2) -> n__add(X1, X2)
  , add(0(), X) -> X
  , add(s(X), Y) -> s(n__add(activate(X), Y))
  , len(X) -> n__len(X)
  , len(nil()) -> 0()
  , len(cons(X, Z)) -> s(n__len(activate(Z))) }
Obligation:
  innermost runtime complexity
Answer:
  MAYBE

The input cannot be shown compatible

Arrrr..