81 lines
2.1 KiB
Plaintext
81 lines
2.1 KiB
Plaintext
import Nevanlinna.meromorphicOn_divisor
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import Nevanlinna.stronglyMeromorphicAt
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import Mathlib.Algebra.BigOperators.Finprod
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open Topology
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/- Strongly MeromorphicOn -/
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def StronglyMeromorphicOn
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(f : ℂ → ℂ)
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(U : Set ℂ) :=
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∀ z ∈ U, StronglyMeromorphicAt f z
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/- Strongly MeromorphicAt is Meromorphic -/
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theorem StronglyMeromorphicOn.meromorphicOn
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{f : ℂ → ℂ}
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{U : Set ℂ}
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(hf : StronglyMeromorphicOn f U) :
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MeromorphicOn f U := by
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intro z hz
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exact StronglyMeromorphicAt.meromorphicAt (hf z hz)
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/- Strongly MeromorphicOn of non-negative order is analytic -/
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theorem StronglyMeromorphicOn.analytic
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{f : ℂ → ℂ}
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{U : Set ℂ}
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(h₁f : StronglyMeromorphicOn f U)
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(h₂f : ∀ x, (hx : x ∈ U) → 0 ≤ (h₁f x hx).meromorphicAt.order):
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∀ z ∈ U, AnalyticAt ℂ f z := by
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intro z hz
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apply StronglyMeromorphicAt.analytic
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exact h₂f z hz
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exact h₁f z hz
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/- Analytic functions are strongly meromorphic -/
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theorem AnalyticOn.stronglyMeromorphicOn
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{f : ℂ → ℂ}
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{U : Set ℂ}
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(h₁f : AnalyticOnNhd ℂ f U) :
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StronglyMeromorphicOn f U := by
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intro z hz
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apply AnalyticAt.stronglyMeromorphicAt
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exact h₁f z hz
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/- Make strongly MeromorphicAt -/
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noncomputable def MeromorphicOn.makeStronglyMeromorphicOn
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{f : ℂ → ℂ}
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{U : Set ℂ}
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(hf : MeromorphicOn f U) :
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ℂ → ℂ := by
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intro z
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by_cases hz : z ∈ U
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· exact (hf z hz).makeStronglyMeromorphicAt z
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· exact f z
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theorem makeStronglyMeromorphicOn_changeDiscrete
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{f : ℂ → ℂ}
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{U : Set ℂ}
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{z₀ : ℂ}
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(hf : MeromorphicOn f U)
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(hz₀ : z₀ ∈ U) :
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hf.makeStronglyMeromorphicOn =ᶠ[𝓝[≠] z₀] f := by
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apply Filter.eventually_iff_exists_mem.2
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let A := (hf z₀ hz₀).eventually_analyticAt
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obtain ⟨V, h₁V, h₂V⟩ := Filter.eventually_iff_exists_mem.1 A
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use V
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constructor
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· assumption
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· intro v hv
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unfold MeromorphicOn.makeStronglyMeromorphicOn
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by_cases h₂v : v ∈ U
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· simp [h₂v]
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rw [← StronglyMeromorphicAt.makeStronglyMeromorphic_id]
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exact AnalyticAt.stronglyMeromorphicAt (h₂V v hv)
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· simp [h₂v]
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