Bogdanskii, Yu. V. “Infinite-Dimensional Version of the Friedrichs Inequality”. Ukrains’kyi Matematychnyi Zhurnal 70, no. 11 (November 25, 2018): 1476-1483. Accessed April 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1651.