Gubreev G. M., and Ignatenko T. R. “On the Class of Orthogonalizators of the Families of Exponents With Real Frequencies”. Ukrains’kyi Matematychnyi Zhurnal 44, no. 8 (September 8, 1992): 1031-1044. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/8031.