GORBACHUK, V. I.; GORBACHUK, M. L. Theory of self-adjoint extensions of symmetric operators. entire operators and boundary-value problems. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 46, n. 1-2, p. 55–62, 1994. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5769. Acesso em: 6 dec. 2025.