Piszczek, Magdalena. “On a Multivalued Second Order Differential Problem With Jensen Multifunction”. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica 8 (June 5, 2009): 31–41. Accessed October 31, 2026. https://studmath.uken.krakow.pl/article/view/13257.