Termination w.r.t. Q proof of TRS/TRCSREx4_Zan97

Termination w.r.t. Q of the following Term Rewriting System could not be shown:

Q restricted rewrite system:
The TRS R consists of the following rules:

a__f(X) → cons(mark(X), f(g(X)))
a__g(0) → s(0)
a__g(s(X)) → s(s(a__g(mark(X))))
a__sel(0, cons(X, Y)) → mark(X)
a__sel(s(X), cons(Y, Z)) → a__sel(mark(X), mark(Z))
mark(f(X)) → a__f(mark(X))
mark(g(X)) → a__g(mark(X))
mark(sel(X1, X2)) → a__sel(mark(X1), mark(X2))
mark(cons(X1, X2)) → cons(mark(X1), X2)
mark(0) → 0
mark(s(X)) → s(mark(X))
a__f(X) → f(X)
a__g(X) → g(X)
a__sel(X1, X2) → sel(X1, X2)

Q is empty.

↳ QTRS

Q restricted rewrite system:
The TRS R consists of the following rules:

a__f(X) → cons(mark(X), f(g(X)))
a__g(0) → s(0)
a__g(s(X)) → s(s(a__g(mark(X))))
a__sel(0, cons(X, Y)) → mark(X)
a__sel(s(X), cons(Y, Z)) → a__sel(mark(X), mark(Z))
mark(f(X)) → a__f(mark(X))
mark(g(X)) → a__g(mark(X))
mark(sel(X1, X2)) → a__sel(mark(X1), mark(X2))
mark(cons(X1, X2)) → cons(mark(X1), X2)
mark(0) → 0
mark(s(X)) → s(mark(X))
a__f(X) → f(X)
a__g(X) → g(X)
a__sel(X1, X2) → sel(X1, X2)

Q is empty.