English
Translating a cusp form by SL(2,Z) gives a cusp form for the SL(2,Z)-modified group.
Русский
Перенос cusp-формы по SL(2,Z) образует cusp-форму для группы, модифицированной SL(2,Z).
LaTeX
$$$[\\text{CuspFormClass} F Γ k] \\to [\\text{CuspForm}(Γ')]$, $Γ' = (toConjAct)^{-1} · Γ$ with $g\\in SL(2,\\mathbb{Z})$.$$
Lean4
theorem bdd_at_infty_slash [ModularFormClass F Γ k] (f : F) (g : SL(2, ℤ)) : IsBoundedAtImInfty (f ∣[k] g) :=
by
rw [← OnePoint.isBoundedAt_infty_iff, SL_slash, ← OnePoint.IsBoundedAt.smul_iff]
apply bdd_at_cusps f
rw [Subgroup.IsArithmetic.isCusp_iff_isCusp_SL2Z, isCusp_SL2Z_iff']
exact ⟨g, by simp [mapGL]⟩