Boichuk ОA, Pokutnyi ОО. Perturbation Theory of Operator Equations in the FréChet and Hilbert Spaces. Ukr. Mat. Zhurn. [Internet]. 2015 Sep. 25 [cited 2025 Dec. 5];67(9):1181-8. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/2057