LAUDAL, O. A.; SLETSJOE, A. Betti numbers of monoid algebras. Applications to 2-dimensional torus imbeddings. Mathematica Scandinavica, Berkeley, CA, United States, v. 56, p. 145–162, 1985. DOI: 10.7146/math.scand.a-12093. Disponível em: https://journals.msp.org/mscand/article/view/1532. Acesso em: 25 jul. 2026.