OsilenkerB. P. “M. G. Krein’s Ideas in the Theory of Orthogonal Polynomials”. Ukrains’kyi Matematychnyi Zhurnal 46, no. 1-2 (February 25, 1994): 76–86. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5771.