Regular maps and principal congruence subgroups of Hecke groups.
The authors continue the study of the relation between the normal subgroups of the Hecke groups and regular maps, started with \textit{G. A. Jones} and \textit{D. Singerman} [Proc. Lond. Math. Soc., III. Ser. 37, 273-307 (1978; Zbl 0391.05024)], and continued with \textit{I. N. Cangül} and \textit{D. Singerman} [Math. Proc. Camb. Philos. Soc. 123, No. 1, 59-74 (1998; Zbl 0893.20036)]. In the former, the existence of a one to one correspondence between the normal subgroups of certain classes of discrete groups and regular maps was established, and in the latter, this correspondence was applied to determine normal subgroups of the Hecke groups. Here the authors consider a similar correspondence between regular maps and principal congruence subgroups of Hecke groups.
scientific article; zbMATH DE number 2142216
scientific article