NIZHNIK, L. P. On point interaction in quantum mechanics. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 49, n. 11, p. 1557–1560, 1997. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5156. Acesso em: 7 apr. 2025.