V. M. Los’, “Systems parabolic in Petrovskii’s sense in Hörmander spaces”, Ukr. Mat. Zhurn., vol. 69, no. 3, pp. 365–380, Mar. 2017, Accessed: Feb. 16, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/1702