Termination of the given GTRS could not be shown:

(0) Obligation:

Generalized rewrite system (where rules with free variables on rhs are allowed):
The TRS R consists of the following rules:

U12(tt) → s(length(L))
zeros → cons(0)
U11(tt) → U12(tt)
length(nil) → 0
length(cons(N)) → U11(tt)