TSVETANOV, M. M. Quality in extremal problems. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 23, n. 2, p. 201–217, 1971. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8502. Acesso em: 6 dec. 2025.