Gorbachuk, V. M., and M. L. Gorbachuk. “Spaces of Smooth and Generalized Vectors of the generator of an Analytic Semigroup and Their Applications”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 69, no. 4, Apr. 2017, pp. 478-09, https://umj.imath.kiev.ua/index.php/umj/article/view/1711.