Bogdanskii, Yu. V. “Boundary Trace Operator in a Domain of Hilbert Space and the Characteristic Property of Its Kernel”. Ukrains’kyi Matematychnyi Zhurnal 67, no. 11 (November 25, 2015): 1450-1460. Accessed April 18, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2081.