Los’, V. M. “Systems Parabolic in Petrovskii’s Sense in Hörmander Spaces”. Ukrains’kyi Matematychnyi Zhurnal 69, no. 3 (March 25, 2017): 365-380. Accessed April 23, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1702.