BerezovskyN. I., and LinchukS. S. “On the Commutant of a Multiplication Operator and Conditions of Invertibility of Its Elements”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 45, no. 1, Jan. 1993, pp. 21–25, https://umj.imath.kiev.ua/index.php/umj/article/view/5777.