Lavrenyuk, Ya. V., and V. I. Sushchanskii. “Lattice of Normal Subgroups of a Group of Local Isometries of the Boundary of a Spherically Homogeneous Tree”. Ukrains’kyi Matematychnyi Zhurnal 60, no. 10 (October 25, 2008): 1350–1356. Accessed April 11, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/3249.