Consider the TRS R consisting of the rewrite rule

1: f(g(X)) -> f(X)

There is one dependency pair:

2: F(g(X)) -> F(X)

The approximated dependency graph contains one SCC:
{2}.

- Consider the SCC {2}.
There are no usable rules.
By taking the polynomial interpretation
[F](x) = [g](x) = x + 1,
rule 2
is strictly decreasing.

Hence the TRS is terminating.