Vakarchuk, S. B. “Best Mean-Square Approximation of Functions Defined on the Real Axis by Entire Functions of Exponential Type”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 64, no. 5, May 2012, pp. 604-15, https://umj.imath.kiev.ua/index.php/umj/article/view/2601.