Lyubich, Yu. I. “Dissipative Actions and Almost Periodical Representations of Abelian Semigroups ”. Ukrains’kyi Matematychnyi Zhurnal, vol. 40, no. 1, Dec. 1987, pp. 70-74, https://umj.imath.kiev.ua/index.php/umj/article/view/9057.