Congruence Subgroups of Groups Commensurable with PSL (2, Z) of Genus 0 and 1
Congruence Subgroups of Groups Commensurable with PSL (2, Z) of Genus 0 and 1
Thompson has shown that up to conjugation there are only finitely many congruence subgroups of PSL(2, R) of fixed genus. For PSL(2, Z), Cox and Parryfound an explicit bound for the level of a congruence subgroup in terms of its genus. This result was used by the author and Pauli …