Using nu_e -> nu_tau: golden and silver channels at the Neutrino Factory

I briefly review the source of the so-called intrinsic ambiguity and show how the combination of ``golden'' and ``silver'' channel at the Neutrino Factory can solve the problem, in the absence of other sources of degeneracies. I then relaxed the hypothesis $\theta_{23} = 45^\circ$ and show how the different dependence of the two channels on $\theta_{23}$ can help in solving the intrinsic and $\theta_{23}$-octant ambiguity at the same time.