PEETRE, J. A generalization of Courant’s nodal domain theorem. MATHEMATICA SCANDINAVICA, [S. l.], v. 5, p. 15–20, 1957. DOI: 10.7146/math.scand.a-10484. Disponível em: https://www.mscand.dk/article/view/10484. Acesso em: 29 apr. 2024.