NYAMORADI, Nemat and ZHOU, Yong. Existence of solutions for a Kirchhoff type fractional differential equations via minimal principle and Morse theory. Topological Methods in Nonlinear Analysis. Online. 1 December 2015. Vol. 46, no. 2, pp. 617 - 630. [Accessed 3 July 2024]. DOI 10.12775/TMNA.2015.061.