Rabanovych, V. I. “On the Decomposition of an Operator into a Sum of Four Idempotents”. Ukrains’kyi Matematychnyi Zhurnal 56, no. 3 (March 25, 2004): 419–424. Accessed April 14, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/3764.