Chabrowski, J., and S. Yan. “The Effect of the Graph Topology on a Semilinear Elliptic Equation With Critical Exponent”. Topological Methods in Nonlinear Analysis, vol. 12, no. 1, Sept. 1998, pp. 1-26, https://apcz.umk.pl/TMNA/article/view/TMNA.1998.025.