Li, Wen Rong, and Sui Sun Cheng. “Wendroff Type Inequalities for Nonlinear Hyperbolic Equations”. Tamkang Journal of Mathematics 32, no. 4 (December 31, 2001): 327–333. Accessed April 20, 2024. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/347.