BerezovskyA. A., MitropolskiyY. A., and NetesovaT. M. “On One Nonlocal Problem With Free Boundary”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 53, no. 7, July 2001, pp. 908-1, https://umj.imath.kiev.ua/index.php/umj/article/view/4312.