Akhmetov , M. U., and N. A. Perestyuk. “Integral Sets of Quasilinear Pulse Systems”. Ukrains’kyi Matematychnyi Zhurnal 44, no. 1 (February 4, 1992): 5–11. Accessed April 7, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/2314.