FENG, Zhenping and DU, Zhuoran. Periodic solutions of fractional Laplace equations: Least period, axial symmetry and limit. Topological Methods in Nonlinear Analysis. Online. 10 December 2022. Vol. 60, no. 2, pp. 633 - 651. [Accessed 27 December 2025]. DOI 10.12775/TMNA.2022.016.