Il'kiv, V.S. “The Smoothness of Solutions of the Problems With Nonlocal Multi-Point Conditions for Strictly Hyperbolic Equations”. Carpathian Mathematical Publications 1, no. 1 (June 30, 2009): 47–58. Accessed November 22, 2024. https://ktipe.pnu.edu.ua/index.php/cmp/article/view/4003.