YURY KOVALEV. Connections the Sobolev spaces and the Hilbert space ℓ2 and their application at point interaction model . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 69, n. 12, p. 1615–1624, 2023. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/6012. Acesso em: 5 dec. 2025.