KovachY. I. (1966) “Theorem of the «fork» in Cauchy’s problem for nonlinear partial differential equations of higher orders”, Ukrains’kyi Matematychnyi Zhurnal, 18(5), pp. 23-35. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/8438 (Accessed: 27July2024).