On the Subgroups of the Triangle Group *2p∞
In this work, we discuss the low index subgroups of the triangle group *2p∞ (also called the extended Hecke group) which were derived using tools in color symmetry theory. Moreover, we present the low index subgroups of the index 2 subgroups of the extended modular group *23∞.
Provido, E. D. B., de las Penas, M. L. A. N., & Decena, M. C. B. (2012). On the Subgroups of the Triangle Group* 2p∞. In Proceedings Of The International Conference On Algebra 2010: Advances in Algebraic Structures (pp. 478-495).