1.
AIZICOVICI, Sergiu, PAPAGEORGIOU, Nikolaos S. & STAICU, Vasile. Existence and multiplicity of solutions for resonant nonlinear Neumann problems. Topological Methods in Nonlinear Analysis [online]. 23 April 2010, T. 35, nr 2, s. 235–252. [accessed 22.1.2022].