EKHOLM, Tobias. Immersions in the metastable range and spin structures on surfaces. Mathematica Scandinavica, Berkeley, CA, United States, v. 83, n. 1, p. 5–41, 1998. DOI: 10.7146/math.scand.a-13840. Disponível em: https://journals.msp.org/mscand/article/view/988. Acesso em: 25 jul. 2026.