VAKARCHUK, S. B.; VAKARCHUK, M. B. $K$-functionals and extreme problems of the theory of approximation of the classes of analytic functions in a circle. II. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 74, n. 7, p. 921–929, 2022. DOI: 10.37863/umzh.v74i7.6981. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/6981. Acesso em: 5 dec. 2025.