GorbachukV. M., and GorbachukM. L. 2017. “Spaces of Smooth and Generalized Vectors of the generator of an Analytic Semigroup and Their Applications”. Ukrains’kyi Matematychnyi Zhurnal 69 (4), 478-509. https://umj.imath.kiev.ua/index.php/umj/article/view/1711.