Moussaoui, Toufik, and Radu Precup. “Positive Solutions for Elliptic Boundary Value Problems With a Harnack-Like Property”. CUBO, A Mathematical Journal 10, no. 4 (December 1, 2008): 109–117. Accessed March 28, 2024. https://cubo.ufro.cl/ojs/index.php/cubo/article/view/1492.