LASSAK, Marek; PRÓSZYNSKI, Andrzej. Algebraic and geometric approach to the classification of semispaces. Mathematica Scandinavica, Berkeley, CA, United States, v. 61, p. 204–212, 1987. DOI: 10.7146/math.scand.a-12199. Disponível em: https://journals.msp.org/mscand/article/view/1475. Acesso em: 25 jul. 2026.