BRUCE, J.W.; GIBLIN, P.J.; TARI, F. Families of surfaces: Height functions and projections to planes. Mathematica Scandinavica, Berkeley, CA, United States, v. 82, n. 2, p. 165–185, 1998. DOI: 10.7146/math.scand.a-13831. Disponível em: https://journals.msp.org/mscand/article/view/997. Acesso em: 25 jul. 2026.