Storozh, O. G., and O. B. Shuvar. 2002. “On One Class of Almost Bounded Perturbations of Smooth Restrictions of a Closed Operator”. Ukrains’kyi Matematychnyi Zhurnal 54 (10): 1396-1402. https://umj.imath.kiev.ua/index.php/umj/article/view/4177.