Ostrovskii, V.L. and Samoilenko, Y.S. (1993) “On pairs of unbounded self-adjoint operators satisfying an algebraic relation”, Ukrains’kyi Matematychnyi Zhurnal, 45(9), pp. 1253–1258. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5927 (Accessed: 5 December 2025).