2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/122524We determine the group structure of the normalizer of $Γ_0(N)$ in $SL_2(\R)$ modulo $Γ_0(N)$. These results correct the Atkin-Lehner statement at the paper Hecke operators of $Γ_0(N)$.Number Theory20H05(19B37,11G18)text