Berger, Melvyn S., et al. “Infinite-Dimensional Singularity Theory and Bifurcation from Equilibria for Certain Nonlinear Evolution Equations”. Topological Methods in Nonlinear Analysis, vol. 4, no. 2, Dec. 1994, pp. 341-53, https://apcz.umk.pl/TMNA/article/view/TMNA.1994.032.