BazaliiB. V., and Vasil’evaN. V. “On the Solvability of the Hele–Shaw Model Problem in Weighted Hölder Spaces in a Plane Angle”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 52, no. 11, Nov. 2000, pp. 1446-57, https://umj.imath.kiev.ua/index.php/umj/article/view/4552.