English
The slash-invariant form f is periodic of width N under horizontal translations by N·n along the vertical direction.
Русский
Форма SlashInvariantForm периодична по ширине N при горизонтальном переносе на N·n вдоль вертикали.
LaTeX
$$$ f(((N \\cdot n) \\mathbin{\\cdot} \\mathbb{R}) +_v z) = f(z) $$$
Lean4
theorem vAdd_width_periodic (N : ℕ) (k n : ℤ) (f : SlashInvariantForm (Gamma N) k) (z : ℍ) :
f (((N * n) : ℝ) +ᵥ z) = f z := by
norm_cast
rw [← modular_T_zpow_smul z (N * n), MulAction.compHom_smul_def, slash_action_eqn']
· simp [-map_zpow, ModularGroup.coe_T_zpow (N * n)]
· simpa using Subgroup.mem_map_of_mem (mapGL ℝ) <| ModularGroup_T_pow_mem_Gamma _ _ (Int.dvd_mul_right N n)