HURSCH, Jack L. Proximity and Height. Mathematica Scandinavica, Berkeley, CA, United States, v. 17, p. 150–160, 1965. DOI: 10.7146/math.scand.a-10769. Disponível em: https://journals.msp.org/mscand/article/view/2554. Acesso em: 25 jul. 2026.