FORTUNA, E.; GALBIATI, M. A counterexample to the seperation of semialgebraic sets. Mathematica Scandinavica, Berkeley, CA, United States, v. 69, p. 161–165, 1991. DOI: 10.7146/math.scand.a-12374. Disponível em: https://journals.msp.org/mscand/article/view/1298. Acesso em: 24 jul. 2026.