BRINCK, Inge. Self-Adjointness and Spectra of Sturm-Liouville Operators. Mathematica Scandinavica, Berkeley, CA, United States, v. 7, p. 219–240, 1959. DOI: 10.7146/math.scand.a-10575. Disponível em: https://journals.msp.org/mscand/article/view/2773. Acesso em: 8 sep. 2026.