Myronyk, V.I., and V.V. Mykhaylyuk. “First-Order Linear Partial Differential Equations in the Class of Separately Differentiable Functions”. Carpathian Mathematical Publications 5, no. 1 (June 20, 2013): 89–93. Accessed November 21, 2024. https://journals.pnu.edu.ua/index.php/cmp/article/view/3655.