StorozhO. G., and ShuvarO. B. “On One Class of Almost Bounded Perturbations of Smooth Restrictions of a Closed Operator”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 54, no. 10, Oct. 2002, pp. 1396-02, https://umj.imath.kiev.ua/index.php/umj/article/view/4177.