-- Mathlib/NumberTheory/LSeries/ZMod.lean
/--
The `LFunction` of the function `x ↦ e (j * x)`, where `e : ZMod N → ℂ` is the standard additive
character, is `expZeta (j / N)`.

Note this is not at all obvious from the definitions, and we prove it by analytic continuation
from the convergence range.
-/
lemma LFunction_stdAddChar_eq_expZeta (j : ZMod N) (s : ℂ) (hjs : j ≠ 0 ∨ s ≠ 1) :
    LFunction (fun k ↦ 𝕖 (j * k)) s = expZeta (ZMod.toAddCircle j) s

Proof state:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
hf : AnalyticOnNhd ℂ f U
hg : AnalyticOnNhd ℂ g U
hUc : IsPreconnected U
hV : V ∈ 𝓝 2
hUmem : 2 ∈ U
hUmem' : s ∈ U
⊢ f =ᶠ[𝓝 2] g

Tactic:
filter_upwards [hV] with z using LFunction_stdAddChar_eq_expZeta_of_one_lt_re _

Result:
no goals

Proof state:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
⊢ LFunction (fun k => 𝕖 (j * k)) s = expZeta (toAddCircle j) s

Tactic:
let g := expZeta (toAddCircle j)

Result:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
⊢ LFunction (fun k => 𝕖 (j * k)) s = expZeta (toAddCircle j) s

Proof state:
case pos
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
hf : AnalyticOnNhd ℂ f U
hg : AnalyticOnNhd ℂ g U
h : j = 0
⊢ IsPreconnected U

Tactic:
simpa only [h, ↓reduceIte, U] using
  (isConnected_compl_singleton_of_one_lt_rank (by simp) _).isPreconnected

Result:
no goals

Proof state:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
hf : AnalyticOnNhd ℂ f U
hg : AnalyticOnNhd ℂ g U
hUc : IsPreconnected U
⊢ 2 ∈ re ⁻¹' Set.Ioi 1

Tactic:
simp

Result:
no goals

Proof state:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
hf : AnalyticOnNhd ℂ f U
hg : AnalyticOnNhd ℂ g U
hUc : IsPreconnected U
hV : V ∈ 𝓝 2
⊢ LFunction (fun k => 𝕖 (j * k)) s = expZeta (toAddCircle j) s

Tactic:
have hUmem : 2 ∈ U := by simp [U]

Result:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
hf : AnalyticOnNhd ℂ f U
hg : AnalyticOnNhd ℂ g U
hUc : IsPreconnected U
hV : V ∈ 𝓝 2
hUmem : 2 ∈ U
⊢ LFunction (fun k => 𝕖 (j * k)) s = expZeta (toAddCircle j) s

Proof state:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
⊢ IsOpen U

Tactic:
by_cases h : j = 0

Result:
case pos
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
h : j = 0
⊢ IsOpen U

case neg
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
h : ¬j = 0
⊢ IsOpen U

Proof state:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
hf : AnalyticOnNhd ℂ f U
hg : AnalyticOnNhd ℂ g U
hUc : IsPreconnected U
⊢ LFunction (fun k => 𝕖 (j * k)) s = expZeta (toAddCircle j) s

Tactic:
have hV : V ∈ 𝓝 2 := (continuous_re.isOpen_preimage _ isOpen_Ioi).mem_nhds (by simp)

Result:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
hf : AnalyticOnNhd ℂ f U
hg : AnalyticOnNhd ℂ g U
hUc : IsPreconnected U
hV : V ∈ 𝓝 2
⊢ LFunction (fun k => 𝕖 (j * k)) s = expZeta (toAddCircle j) s

Proof state:
case neg
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
h : ¬j = 0
⊢ IsOpen U

Tactic:
simp only [h, ↓reduceIte, isOpen_univ, U]

Result:
no goals

Proof state:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
hf : AnalyticOnNhd ℂ f U
hg : AnalyticOnNhd ℂ g U
hUc : IsPreconnected U
hV : V ∈ 𝓝 2
hUmem : 2 ∈ U
hUmem' : s ∈ U
⊢ LFunction (fun k => 𝕖 (j * k)) s = expZeta (toAddCircle j) s

Tactic:
refine hf.eqOn_of_preconnected_of_eventuallyEq hg hUc hUmem ?_ hUmem'

Result:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
hf : AnalyticOnNhd ℂ f U
hg : AnalyticOnNhd ℂ g U
hUc : IsPreconnected U
hV : V ∈ 𝓝 2
hUmem : 2 ∈ U
hUmem' : s ∈ U
⊢ f =ᶠ[𝓝 2] g

Proof state:
case neg
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
hf : AnalyticOnNhd ℂ f U
hg : AnalyticOnNhd ℂ g U
h : ¬j = 0
⊢ IsPreconnected U

Tactic:
simpa only [h, ↓reduceIte, U] using isPreconnected_univ

Result:
no goals

Proof state:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
⊢ LFunction (fun k => 𝕖 (j * k)) s = expZeta (toAddCircle j) s

Tactic:
have hf : AnalyticOnNhd ℂ f U := by
  refine DifferentiableOn.analyticOnNhd (fun u hu ↦ ?_) hUo
  refine (differentiableAt_LFunction _ _ ((hU.mp hu).imp_right fun h ↦ ?_)).differentiableWithinAt
  simp only [mul_comm j, AddChar.sum_mulShift _ (isPrimitive_stdAddChar _), h,
    ↓reduceIte, CharP.cast_eq_zero, or_true]

Result:
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
hUo : IsOpen U
f : ℂ → ℂ := LFunction fun k => 𝕖 (j * k)
g : ℂ → ℂ := expZeta (toAddCircle j)
hU : ∀ {u : ℂ}, u ∈ U ↔ u ≠ 1 ∨ j ≠ 0
hf : AnalyticOnNhd ℂ f U
⊢ LFunction (fun k => 𝕖 (j * k)) s = expZeta (toAddCircle j) s

Proof state:
case pos
N : ℕ
inst✝ : NeZero N
j : ZMod N
s : ℂ
hjs : j ≠ 0 ∨ s ≠ 1
U : Set ℂ := if j = 0 then {z | z ≠ 1} else Set.univ
V : Set ℂ := {z | 1 < z.re}
h : j = 0
⊢ IsOpen U

Tactic:
simpa only [h, ↓reduceIte, U] using isOpen_compl_singleton

Result:
no goals