Veliev, S. G., and S. S. Mirzoev. “On Solutions of One Class of Second-Order Operator Differential Equations in the Class of Holomorphic Vector Functions”. Ukrains’kyi Matematychnyi Zhurnal 62, no. 6 (June 25, 2010): 801–813. Accessed May 4, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2911.