BOIKO, C. C.; DUBOVOI, V. K.; KIRSTEIN, B.; FRITZSCHE, B. Contraction operators, defect functions, and scattering theory. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 49, n. 4, p. 481–489, 1997. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5021. Acesso em: 7 apr. 2025.