We relate Kaptsov's method of B-determining equations for finding invariant solutions of PDEs to the nonclassical method and to the method of generalised conditional symmetries. An extension of Kaptsov's method is then used to find new solutions of degenerate diffusion equations.
Goard, J. M. (2000). The method of generalised conditional symmetries and its various implementations. European Journal of Applied Mathematics, 11 (2), 215-224.