  Consider the fixed-$\ell$ inverse scattering problem. We show that the zeros
of the regular solution of the Schr\"odinger equation, $r_{n}(E)$, which are
monotonic functions of the energy, determine a unique potential when the domain
of the energy is such that the $r_{n}(E)$ range from zero to infinity. This
suggests that the use of the mixed data of phase-shifts
  $\{\delta(\ell_0,k), k \geq k_0 \} \cup \{\delta(\ell,k_0), \ell \geq \ell_0
\}$, for which the zeros of the regular solution are monotonic in both domains,
and range from zero to infinity, offers the possibility of determining the
potential in a unique way.
