Koshmanenko, V. D. and Tuhai, H. V. (2004) “On the structure of resolvent of singularly perturbed operator solving the problem of eigenvalues”, Ukrains’kyi Matematychnyi Zhurnal, 56(9), pp. 1292-1297. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/3843 (Accessed: 3May2024).