Kengne, E. “Well-Posed and Regular Nonlocal Boundary-Value Problems for Partial Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal 54, no. 8 (August 25, 2002): 1135-1142. Accessed May 9, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4152.