Ren J, Zhai C. Some properties of sets, fixed point theorems in ordered product spaces and applications to a nonlinear system of fractional differential equations. TMNA [Internet]. 26 maj 2017 [cytowane 22 lipiec 2024];49(2):625-4. Dostępne na: https://apcz.umk.pl/TMNA/article/view/TMNA.2016.095