ZIZLER, Václav. On Some Extremal Problems in Banach Spaces. MATHEMATICA SCANDINAVICA, [S. l.], v. 32, p. 214–224, 1973. DOI: 10.7146/math.scand.a-11456. Disponível em: https://tidsskrift.dk/math/article/view/11456. Acesso em: 14 aug. 2026.