JOHNSEN, Trygve. Multiplicities of solutions to some enumerative contact problems. Mathematica Scandinavica, Berkeley, CA, United States, v. 63, p. 87–108, 1988. DOI: 10.7146/math.scand.a-12226. Disponível em: https://journals.msp.org/mscand/article/view/1441. Acesso em: 24 jul. 2026.