Nomirovs’kii, D. A. “On Homeomorphisms Realized by Certain Partial Differential Operators”. Ukrains’kyi Matematychnyi Zhurnal 56, no. 12 (December 25, 2004): 1707-1716. Accessed May 10, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3878.