Candela, Anna Maria, Everaldo Souto de Medeiros, Giuliana Palmieri, and Kanishka Perera. 2010. “Weak Solutions of Quasilinear Elliptic Eystems via the Cohomological Index”. Topological Methods in Nonlinear Analysis 36 (1):1-18. https://apcz.umk.pl/TMNA/article/view/TMNA.2010.024.