PEETRE, Jaak. A generalization of Courant’s nodal domain theorem. Mathematica Scandinavica, Berkeley, CA, United States, v. 5, p. 15–20, 1957. DOI: 10.7146/math.scand.a-10484. Disponível em: https://journals.msp.org/mscand/article/view/2839. Acesso em: 25 jul. 2026.