Bilichenko, R. O., and V. F. Babenko. “Refinement of a Hardy–Littlewood–Pólya-Type Inequality for Powers of Self-Adjoint Operators in a Hilbert Space”. Ukrains’kyi Matematychnyi Zhurnal 61, no. 10 (October 25, 2009): 1299-1305. Accessed March 29, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3101.