WATTENBERG, Frank. Differentiable Motions of Unknotted, Unlinked Circles in 3-Space. Mathematica Scandinavica, Berkeley, CA, United States, v. 30, p. 107–135, 1972. DOI: 10.7146/math.scand.a-11068. Disponível em: https://journals.msp.org/mscand/article/view/2259. Acesso em: 25 jul. 2026.