On the Riesz Means of Expansions by Riesz Bases Formed by Eigenfunctions for the Ordinary Differential Operator of 4-th Order. IHJPAS [Internet]. 2017 Aug. 16 [cited 2024 May 19];22(1). Available from: https://jih.uobaghdad.edu.iq/index.php/j/article/view/1277