Termination of the given GTRS could be disproven:

(0) Obligation:

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

sel(0, cons) → X
sel(s, cons) → sel(X, Z)
dbl(0) → 0
dbl(s) → s
dbls(nil) → nil
dbls(cons) → cons
indx(nil) → nil
indx(cons) → cons
from → cons

(1) CritRuleProof (EQUIVALENT transformation)

The rule sel(0, cons) → X contains free variables in its right-hand side. Hence the TRS is not-terminating.

(2) NO