ALBEVERIO, S.; KOSHMANENKO, V. D.; MAKAROV, K. A. Generalized eigenfunctions under singular perturbation. Methods of Functional Analysis and Topology, [S. l.], v. 5, n. 1, p. 13–28, 1999. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/79. Acesso em: 17 dec. 2025.