DYMARSKIĬ, Yakov and NEPIYPA, Dmytriĭ. Bifurcation in the case of twofold degeneration. The quasi-linear approach. Topological Methods in Nonlinear Analysis. Online. 23 April 2011. Vol. 38, no. 1, pp. 169 - 186. [Accessed 22 July 2024].