Mikhailets, V. A., and A. A. Murach. “Improved Scales of Spaces and Elliptic Boundary-Value Problems. I”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, no. 2, Feb. 2006, pp. 217–235, https://umj.imath.kiev.ua/index.php/umj/article/view/3448.