Baranetsky , Y.O. (1992) “Similar operators generated by the nonlocal problems for elliptical second-order equations ”, Ukrains’kyi Matematychnyi Zhurnal, 44(9), pp. 1174–1181. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/8166 (Accessed: 14 April 2025).