Tetragonal modular curves
On the arithmetic of certain modular curves
Bielliptic modular curves X₁(N)
On the torsion of elliptic curves over cubic number fields
Normalizers of intermediate congruence subgroups of the Hecke subgroups
For a square-free positive integer N, we study the normalizer of ΓΔ(N) in PSL2(ℝ) and investigate the group structure of its quotient by ΓΔ(N) under certain conditions.
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