LASSAK, M.; PRÓSZYNSKI, A. Algebraic and geometric approach to the classification of semispaces. MATHEMATICA SCANDINAVICA, [S. l.], v. 61, p. 204–212, 1987. DOI: 10.7146/math.scand.a-12199. Disponível em: https://www.mscand.dk/article/view/12199. Acesso em: 7 may. 2024.