The automorphism group of the modular curve 𝑋₀*(𝑁) with square-free level

Bars, Francesc; González, Josep

doi:10.1090/tran/8391

The automorphism group of the modular curve $X_0^*(N)$ with square-free level
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Trans. Amer. Math. Soc. 374 (2021), 5783-5803 Request permission

Abstract:

We determine the automorphism group of the modular curve $X_0^*(N)$, obtained as the quotient of the modular curve $X_0(N)$ by the group of its Atkin-Lehner involutions, for all square-free values of $N$.

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