OGURISU, O. On the number of negative eigenvalues of a multi-dimensional Schrodinger operator with point interactions. Methods of Functional Analysis and Topology, [S. l.], v. 16, n. 4, p. 383–392, 2010. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/464. Acesso em: 16 dec. 2025.