  The experimental determination of low energy pi K scattering phase shifts
would assist in determining scattering lengths as well as low energy constants
of chiral perturbation theory for which sum rules have been constructed. The
FOCUS collaboration has presented evidence for interference pheomena from their
analysis of D_l4 decays based on decay amplitudes suitable for a cascade decay
D -> K* -> K pi. We point out that if the well-known full five body kinematics
are taken into account, pi K scattering phases may be extracted. We also point
out that other distributions considered in the context of K_l4 decays can be
applied to charm meson decays to provide constraints on violation of |Delta
I|=1/2 rule and T-violation.
