SHABOZOV, M. Sh. Best approximation and best unilateral approximation of the kernel of a biharmonic equation and optimal renewal of the values of operators. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 47, n. 11, p. 1549–1557, 1995. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5546. Acesso em: 5 dec. 2025.