[1]
Y. M. Berezansky and J. F. Brasche, “Generalized selfadjoint operators and their singular perturbations”, MFAT, vol. 8, no. 4, pp. 1–14, Dec. 2002, Accessed: Dec. 17, 2025. [Online]. Available: https://zen.imath.kiev.ua/index.php/mfat/article/view/197