1. Hecke operators on Γ0(m);Atkin;Math. Ann.,1970
2. The normaliser of Γ0(N) in PSL2(ℝ);Akbas;Glasgow Math. J.,1990
3. The invariants of the congruence subgroups G0(P) of the Hecke group;Chan;Illinois J. Math.,1994
4. Understanding groups like Γ0(N);Conway,1993
5. Monstrous Moonshine;Conway;Bull. London Math. Soc.,1979