The automorphism group of the modular curve $X_0^*(N)$ with square-free level

Francesc Bars, Josep González

Published 2020-07-08Version 1

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 $N$.