NepritvorennayaL. M. “Determination of Unknown Parameters under Conformal Mapping of the Upper Half-Plane on an Arbitrary Circular Quadrangle ”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 23, no. 2, Feb. 1971, pp. 261-8, https://umj.imath.kiev.ua/index.php/umj/article/view/8512.