KLIMCZAK, L. Two constant sign solutions for a nonhomogeneous Neumann boundary value problem. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica, [S. l.], v. 14, p. 47–62, 2015. Disponível em: https://studmath.uken.krakow.pl/article/view/13153. Acesso em: 31 oct. 2026.