Byszewski, Ludwik. “Strong Maximum Principles for Implicit Parabolic Functional-Differential Problems Together With Initial Inequalities”. Annales Universitatis Paedagogicae Cracoviensis Studia Mathematica 4 (May 22, 2004): 9–16. Accessed October 31, 2026. https://studmath.uken.krakow.pl/article/view/13304.