Bazalii, B. V. “On One Proof of the Classical Solvability of the Hele-Shaw Problem With Free Boundary”. Ukrains’kyi Matematychnyi Zhurnal, vol. 50, no. 11, Nov. 1998, pp. 1452–1462, https://umj.imath.kiev.ua/index.php/umj/article/view/4797.