Termination proof of /tmp/tmp5rcGse/ExIntrod_GM04

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:

hd(cons) → X
tl(cons) → Y
nats → adx(zeros)
zeros → cons
incr(cons) → cons
adx(cons) → incr(cons)

↳ GTRS

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

hd(cons) → X
tl(cons) → Y
nats → adx(zeros)
zeros → cons
incr(cons) → cons
adx(cons) → incr(cons)