STYPUŁA, Tomasz; WÓJCIK, Paweł. Characterizations of rotundity and smoothness by approximate orthogonalities. Annales Mathematicae Silesianae, [S. l.], v. 30, p. 193–201, 2016. Disponível em: https://trrest.vot.pl/ojsus/index.php/AMSIL/article/view/13963. Acesso em: 8 may. 2025.