Comment on "Wave Refraction in Negative-Index Media: Always Positive and   Very Inhomogeneous"
  In a recent Physical Review Letter [1] Valanju Walser and Valanju (VWV) called into question the basis of work on the so called negative index media (NIM). See for example [2,3]. The key point at issue is, `what is the group velocity of a wave in NIM?' 
JB Pendry and D.R. Smith