MATTSON, Don A. Dense $p$-Subspaces of Proximity Spaces. Mathematica Scandinavica, Berkeley, CA, United States, v. 27, p. 223–226, 1970. DOI: 10.7146/math.scand.a-11000. Disponível em: https://journals.msp.org/mscand/article/view/2327. Acesso em: 25 jul. 2026.