Comment on ''Acoustic solitons in inhomogeneous pair-ion plasmas'' [Phys. Plasmas 17, 122302 (2010)]

Using a standard reductive perturbation technique, Shah et al.[Phys. Plasmas 17, 122302 (2010)] derived a Korteweg-de Vries like equation, with an additional term due to the assumed equilibrium density and flow inhomogeneities in a pair-ion plasma. Unfortunately, a basic flaw at the beginning of the derivation invalidates the whole analysis: their model only supports homogeneous densities and flows in the undisturbed conditions.