KovachY. I. “Theorem of the «fork» in Cauchy’s Problem for Nonlinear Partial Differential Equations of Higher Orders”. Ukrains’kyi Matematychnyi Zhurnal 18, no. 5 (August 31, 1966): 23-35. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/8438.