  Sardar et al. [Phys. Plasmas 23, 073703 (2016)] have studied the stability of
small amplitude dust ion acoustic solitary waves in a collisionless
unmagnetized electron - positron - ion - dust plasma. They have derived a
Kadomtsev Petviashvili (KP) equation to investigate the lowest - order
stability of the solitary wave solution of the Korteweg-de Vries (KdV) equation
for long-wavelength plane-wave transverse perturbation when the weak dependence
of the spatial coordinates perpendicular to the direction of propagation of the
wave is taken into account. In the present paper, we have extended the lowest -
order stability analysis of KdV solitons given in the paper of Sardar et al.
[Phys. Plasmas 23, 073703 (2016)] to higher order with the help of
multiple-scale perturbation expansion method of Allen and Rowlands [J. Plasma
Phys. 50, 413 (1993); 53, 63 (1995)]. It is found that solitary wave solution
of the KdV equation is stable at the order k^2, where k is the wave number for
long-wavelength plane-wave perturbation.
