SamoilenkoY. S., and YakymenkoD. Y. “Scalar Operators Equal to the Product of Unitary Roots of the Identity Operator”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 64, no. 6, June 2012, pp. 819-25, https://umj.imath.kiev.ua/index.php/umj/article/view/2619.