FABRICIUS-BJERRE, Fr. On the Double Tangents of Plane Closed Curves. Mathematica Scandinavica, Berkeley, CA, United States, v. 11, p. 113–116, 1962. DOI: 10.7146/math.scand.a-10656. Disponível em: https://journals.msp.org/mscand/article/view/2693. Acesso em: 25 jul. 2026.