NICHOLS, R.; HOFMANN, S.; GESZTESY, F. On square root domains for non-self-adjoint Sturm-Liouville operators. Methods of Functional Analysis and Topology, [S. l.], v. 19, n. 3, p. 227–259, 2013. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/550. Acesso em: 16 dec. 2025.