Boiko CC, Dubovoi VK, Kirstein B, Fritzsche B. Contraction operators, defect functions, and scattering theory. Ukr. Mat. Zhurn. [Internet]. 1997 Apr. 25 [cited 2025 Apr. 7];49(4):481–489. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/5021