R. Bozhok, S. Albeverio, M. E. Dudkin, and V. D. Koshmanenko, “Dense subspaces in scales of Hilbert spaces”, MFAT, vol. 11, no. 2, pp. 156–169, Jun. 2005, Accessed: Dec. 16, 2025. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/274