English
Translating a cusp form by SL(2,ℤ) yields a cusp form with the transformed group.
Русский
Перенос cusp-формы по SL(2,ℤ) даёт cusp-форму для преобразованной группы.
LaTeX
$$$[\\text{CuspFormClass F Γ k}] (g) : CuspForm( toConjAct(g^{-1})·Γ, k)$ such that translation is compatible with SL(2,ℤ).$$
Lean4
theorem zero_at_infty_slash [CuspFormClass F Γ k] (f : F) (g : SL(2, ℤ)) : IsZeroAtImInfty (f ∣[k] g) :=
by
rw [← OnePoint.isZeroAt_infty_iff, SL_slash, ← OnePoint.IsZeroAt.smul_iff]
apply zero_at_cusps f
rw [Subgroup.IsArithmetic.isCusp_iff_isCusp_SL2Z, isCusp_SL2Z_iff']
exact ⟨g, by simp [mapGL]⟩