PrykarpatskyA.K., SamoilenkoA.M. and SamoilenkoV.G. 2003. Lyapunov–Schmidt Approach to Studying Homoclinic Splitting in Weakly Perturbed Lagrangian and Hamiltonian Systems. Ukrains’kyi Matematychnyi Zhurnal. 55, 1 (Jan. 2003), 66-74.