Ashyralyev, A., and F. Emharab. “Identification Hyperbolic Problems With the Neumann Boundary Condition”. Bulletin of the Karaganda University. Mathematics Series 91, no. 3 (September 29, 2018): 89–98. Accessed July 10, 2025. https://mts.buketov.edu.kz/index.php/mathematics-vestnik/article/view/296.