Gorbachuk O. L., and Yakonska N. O. “Existence of the Boundary in the Chesaro Sense of a Limited Solution of the Evolution Equation in the Banach Space”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 44, no. 9, Oct. 1992, pp. 1279-80, https://umj.imath.kiev.ua/index.php/umj/article/view/8181.