Comment on ``$T$-dependence of the magnetic penetration depth in   unconventional superconductors at low temperatures: Can it be linear?"
  We comment on a recent letter by Schopohl and Dolgov (SD) which raised the possibility that a d-wave superconductor might be thermodynamically unstable in the limit $T\to 0$. The point of our comment is that this instability can be inevitably prevented by the non-local effects. 
P.J. Hirschfeld, M. -R. Li and P. W\"olfle