-- Mathlib/Analysis/Meromorphic/Order.lean
/-- The order of a meromorphic function `f` at a `z₀` is infinity iff `f` vanishes locally around
`z₀`. -/
lemma order_eq_top_iff {f : 𝕜 → E} {x : 𝕜} (hf : MeromorphicAt f x) :
    hf.order = ⊤ ↔ ∀ᶠ z in 𝓝[≠] x, f z = 0

Proof state:
case neg.intro
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
m : ℕ
hm : ↑m = ⋯.order
h : ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0
⊢ ∃ᶠ (z : 𝕜) in 𝓝[≠] x, (z - x) ^ Exists.choose hf • f z = 0

Tactic:
apply Eventually.frequently

Result:
case neg.intro.h
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
m : ℕ
hm : ↑m = ⋯.order
h : ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0
⊢ ∀ᶠ (x_1 : 𝕜) in 𝓝[≠] x, (x_1 - x) ^ Exists.choose hf • f x_1 = 0

Proof state:
case pos
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ⋯.order = ⊤
⊢ ∀ᶠ (x_1 : 𝕜) in 𝓝 x, x_1 ∈ {x}ᶜ → f x_1 = 0

Tactic:
rw [AnalyticAt.order_eq_top_iff] at h

Result:
case pos
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ∀ᶠ (z : 𝕜) in 𝓝 x, (z - x) ^ Exists.choose hf • f z = 0
⊢ ∀ᶠ (x_1 : 𝕜) in 𝓝 x, x_1 ∈ {x}ᶜ → f x_1 = 0

Proof state:
case pos
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ⋯.order = ⊤
⊢ ENat.map (fun x => ↑x) ⋯.order - ↑(Exists.choose hf) = ⊤ ↔ ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0

Tactic:
rw [h, ENat.map_top, ← WithTop.coe_natCast,
  top_sub, eq_self, true_iff, eventually_nhdsWithin_iff]

Result:
case pos
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ⋯.order = ⊤
⊢ ∀ᶠ (x_1 : 𝕜) in 𝓝 x, x_1 ∈ {x}ᶜ → f x_1 = 0

Proof state:
case neg.intro
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ¬⋯.order = ⊤
m : ℕ
hm : ↑m = ⋯.order
⊢ ¬∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0

Tactic:
contrapose! h

Result:
case neg.intro
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
m : ℕ
hm : ↑m = ⋯.order
h : ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0
⊢ ⋯.order = ⊤

Proof state:
case neg.intro
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ¬⋯.order = ⊤
m : ℕ
hm : ↑m = ⋯.order
⊢ ENat.map (fun x => ↑x) ⋯.order - ↑(Exists.choose hf) = ⊤ ↔ ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0

Tactic:
simp only [← hm, ENat.map_coe, WithTop.coe_natCast, sub_eq_top_iff, WithTop.natCast_ne_top,
  or_self, false_iff]

Result:
case neg.intro
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ¬⋯.order = ⊤
m : ℕ
hm : ↑m = ⋯.order
⊢ ¬∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0

Proof state:
case h
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf✝ : MeromorphicAt f x
h : ∀ᶠ (z : 𝕜) in 𝓝 x, (z - x) ^ Exists.choose hf✝ • f z = 0
z : 𝕜
hf : (z - x) ^ Exists.choose hf✝ • f z = 0
hz : z ∈ {x}ᶜ
⊢ f z = 0

Tactic:
rwa [smul_eq_zero_iff_right <| pow_ne_zero _ (sub_ne_zero.mpr hz)] at hf

Result:
no goals

Proof state:
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
⊢ hf.order = ⊤ ↔ ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0

Tactic:
unfold order

Result:
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
⊢ ENat.map (fun x => ↑x) ⋯.order - ↑(Exists.choose hf) = ⊤ ↔ ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0

Proof state:
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
⊢ ENat.map (fun x => ↑x) ⋯.order - ↑(Exists.choose hf) = ⊤ ↔ ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0

Tactic:
by_cases h : hf.choose_spec.order = ⊤

Result:
case pos
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ⋯.order = ⊤
⊢ ENat.map (fun x => ↑x) ⋯.order - ↑(Exists.choose hf) = ⊤ ↔ ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0

case neg
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ¬⋯.order = ⊤
⊢ ENat.map (fun x => ↑x) ⋯.order - ↑(Exists.choose hf) = ⊤ ↔ ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0

Proof state:
case pos
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ∀ᶠ (z : 𝕜) in 𝓝 x, (z - x) ^ Exists.choose hf • f z = 0
⊢ ∀ᶠ (x_1 : 𝕜) in 𝓝 x, x_1 ∈ {x}ᶜ → f x_1 = 0

Tactic:
filter_upwards [h] with z hf hz

Result:
case h
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf✝ : MeromorphicAt f x
h : ∀ᶠ (z : 𝕜) in 𝓝 x, (z - x) ^ Exists.choose hf✝ • f z = 0
z : 𝕜
hf : (z - x) ^ Exists.choose hf✝ • f z = 0
hz : z ∈ {x}ᶜ
⊢ f z = 0

Proof state:
case neg
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ¬⋯.order = ⊤
⊢ ENat.map (fun x => ↑x) ⋯.order - ↑(Exists.choose hf) = ⊤ ↔ ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0

Tactic:
obtain ⟨m, hm⟩ := ENat.ne_top_iff_exists.mp h

Result:
case neg.intro
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
h : ¬⋯.order = ⊤
m : ℕ
hm : ↑m = ⋯.order
⊢ ENat.map (fun x => ↑x) ⋯.order - ↑(Exists.choose hf) = ⊤ ↔ ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0

Proof state:
case neg.intro
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
m : ℕ
hm : ↑m = ⋯.order
h : ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0
⊢ ⋯.order = ⊤

Tactic:
rw [AnalyticAt.order_eq_top_iff]

Result:
case neg.intro
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
m : ℕ
hm : ↑m = ⋯.order
h : ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0
⊢ ∀ᶠ (z : 𝕜) in 𝓝 x, (z - x) ^ Exists.choose hf • f z = 0

Proof state:
case neg.intro
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
m : ℕ
hm : ↑m = ⋯.order
h : ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0
⊢ ∀ᶠ (z : 𝕜) in 𝓝 x, (z - x) ^ Exists.choose hf • f z = 0

Tactic:
rw [← hf.choose_spec.frequently_eq_iff_eventually_eq analyticAt_const]

Result:
case neg.intro
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
m : ℕ
hm : ↑m = ⋯.order
h : ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0
⊢ ∃ᶠ (z : 𝕜) in 𝓝[≠] x, (z - x) ^ Exists.choose hf • f z = 0

Proof state:
case h
𝕜 : Type u_1
inst✝² : NontriviallyNormedField 𝕜
E : Type u_2
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace 𝕜 E
f : 𝕜 → E
x : 𝕜
hf : MeromorphicAt f x
m : ℕ
hm : ↑m = ⋯.order
h : ∀ᶠ (z : 𝕜) in 𝓝[≠] x, f z = 0
z : 𝕜
hfz : f z = 0
⊢ (z - x) ^ Exists.choose hf • f z = 0

Tactic:
rw [hfz, smul_zero]

Result:
no goals