Lavrent'ev, A. S., and Yu. S. Mishura. “The Hille-Yosida Theorem for Resolvent Operators of Multiparameter Semigroups”. Ukrains’kyi Matematychnyi Zhurnal, vol. 48, no. 1, Jan. 1996, pp. 57-65, https://umj.imath.kiev.ua/index.php/umj/article/view/5363.