Nonlinear evolution equations, rescalings, model PDEs and their integrability: II

For pt. I see ibid., vol.3, p.229-62, 1987. The authors continue their investigation of the model equations that govern the wave modulations induced by weakly nonlinear effects, in the context of nonlinear evolution equations in 1+1 dimensions having a dispersive linear part. They study mainly evolution equations with an even linear part (namely, with a linear part that features only derivatives of even order). They identify several model equations, including some that they had found previously and some new ones. They also indicate how one can relate the two classes of nonlinear evolution equations with even and odd linear parts.