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:

U11(tt) → s(length(L))
and(tt) → X
zeros → cons(0)
isNat → tt
isNat → isNatList
isNat → isNat
isNatIList → isNatList
isNatIList → tt
isNatIList → and(isNat)
isNatList → tt
isNatList → and(isNat)
length(nil) → 0
length(cons(N)) → U11(and(isNatList))