KISELMAN, Christer O. Smoothness of vector sums of plane convex sets. Mathematica Scandinavica, Berkeley, CA, United States, v. 60, p. 239–252, 1987. DOI: 10.7146/math.scand.a-12183. Disponível em: https://journals.msp.org/mscand/article/view/1447. Acesso em: 25 jul. 2026.