Termination proof of /tmp/tmp1_-5kF/PALINDROME_nosorts

Termination of the following Term Rewriting System could not be shown:

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

and(tt) → X
__(__(X, Y), Z) → __(X, __(Y, Z))
__(X, nil) → X
__(nil, X) → X
isNePal(__(I, __(P, I))) → tt

↳ GTRS

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

and(tt) → X
__(__(X, Y), Z) → __(X, __(Y, Z))
__(X, nil) → X
__(nil, X) → X
isNePal(__(I, __(P, I))) → tt