Takhirov, Z. O., and R. N. Turaev. “Problem With Nonlocal Condition on the Free Boundary”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 64, no. 1, Jan. 2012, pp. 71-80, https://umj.imath.kiev.ua/index.php/umj/article/view/2556.