VAKARCHUK, S. B.; VAKARCHUK, M. B. $K$-functionals and extreme problems of the theory of approximation for classes of analytic functions in the circle. I. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 74, n. 4, p. 469–485, 2022. DOI: 10.37863/umzh.v74i4.6980. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/6980. Acesso em: 8 dec. 2025.