41 lines
1.4 KiB
Plaintext
41 lines
1.4 KiB
Plaintext
import Mathlib.Analysis.Calculus.LineDeriv.Basic
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import Mathlib.Analysis.Complex.RealDeriv
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variable {z : ℂ} {f : ℂ → ℂ}
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theorem CauchyRiemann₁ : (DifferentiableAt ℂ f z)
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→ (fderiv ℝ f z) Complex.I = Complex.I * (fderiv ℝ f z) 1 := by
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intro h
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rw [DifferentiableAt.fderiv_restrictScalars ℝ h]
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nth_rewrite 1 [← mul_one Complex.I]
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exact ContinuousLinearMap.map_smul_of_tower (fderiv ℂ f z) Complex.I 1
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theorem CauchyRiemann₂ : (DifferentiableAt ℂ f z)
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→ lineDeriv ℝ f z Complex.I = Complex.I * lineDeriv ℝ f z 1 := by
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intro h
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rw [DifferentiableAt.lineDeriv_eq_fderiv (h.restrictScalars ℝ)]
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rw [DifferentiableAt.lineDeriv_eq_fderiv (h.restrictScalars ℝ)]
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exact CauchyRiemann₁ h
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theorem CauchyRiemann₃ : (DifferentiableAt ℂ f z)
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→ (lineDeriv ℝ (Complex.reCLM ∘ f) z 1 = lineDeriv ℝ (Complex.imCLM ∘ f) z Complex.I)
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∧ (lineDeriv ℝ (Complex.reCLM ∘ f) z Complex.I = -lineDeriv ℝ (Complex.imCLM ∘ f) z 1)
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:= by
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intro h
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have ContinuousLinearMap.comp_lineDeriv : ∀ w : ℂ, ∀ l : ℂ →L[ℝ] ℝ, lineDeriv ℝ (l ∘ f) z w = l ((fderiv ℝ f z) w) := by
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intro w l
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rw [DifferentiableAt.lineDeriv_eq_fderiv]
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rw [fderiv.comp]
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simp
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fun_prop
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exact h.restrictScalars ℝ
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apply (ContinuousLinearMap.differentiableAt l).comp
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exact h.restrictScalars ℝ
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repeat
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rw [ContinuousLinearMap.comp_lineDeriv]
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rw [CauchyRiemann₁ h, Complex.I_mul]
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simp
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