ALBER , Ya. I.; NOTIK , A. I. On inequalities of the parallelogram in the Banach space and certain properties of dual mapping. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 40, n. 6, p. 769–771, 1988. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/9288. Acesso em: 7 dec. 2025.