Adamowicz, T., i A. Kałamajska. „On a Variant of the Maximum Principle Involving Radial $p$-Laplacian With Applications to~nonlinear Eigenvalue Problems and Nonexistence Results”. Topological Methods in Nonlinear Analysis, t. 36, nr 1, wrzesień 2009, s. 1-20, https://apcz.umk.pl/TMNA/article/view/TMNA.2009.026.