# Automorphisms

## `CanonicalInvolution(X): CrvMod -> MapSch`

## `AtkinLehnerInvolution(X, N): CrvMod, RngIntElt -> MapSch`

Given a projective modular curve $X = X_0(N)$, the function returns the Atkin-Lehner involution of the modular curve as a map of schemes. Currently, the only Atkin-Lehner involution returned is that for $N$ equal to the level of $X$.