From fbe5000a264f7eaee4c97950e8de237f766f26a6 Mon Sep 17 00:00:00 2001
From: Stefan Kebekus <kebekus@users.noreply.github.com>
Date: Mon, 16 Mar 2026 06:57:02 +0100
Subject: [PATCH] Next challenge

---
 Aristotle/Basic.lean | 97 ++++++++------------------------------------
 1 file changed, 16 insertions(+), 81 deletions(-)

diff --git a/Aristotle/Basic.lean b/Aristotle/Basic.lean
index c4cbaf2..dcccef4 100644
--- a/Aristotle/Basic.lean
+++ b/Aristotle/Basic.lean
@@ -1,88 +1,23 @@
 import Mathlib
 
-open Complex ComplexConjugate Real
+open Complex ComplexConjugate Metric Real
 
-variable {R : ℝ} {w : ℂ}
+variable {R : ℝ} {w p : ℂ}
 
-/-!
-## Blaschke Factors
+noncomputable def herglotzRieszKernel (c w z : ℂ) : ℂ :=
+  ((z - c) + (w - c)) / ((z - c) - (w - c))
 
-Given `R : ℝ` and `w : ℂ`, the Blaschke factor `Blaschke R w : ℂ → ℂ` is
-meromorphic in normal form, has a single pole at `w`, no zeros, and takes values
-of norm one on the circle of radius `R`.
--/
+lemma herglotzRieszKernel_def (c w z : ℂ) :
+    herglotzRieszKernel c w z = ((z - c) + (w - c)) / ((z - c) - (w - c)) := by rfl
 
-noncomputable def Blaschke (R : ℝ) (w : ℂ) : ℂ → ℂ :=
-  fun z ↦ (R ^ 2 - (conj w) * z) / (R * (z - w))
-
-lemma meromorphicOn_blaschke (R : ℝ) (w : ℂ) :
-    MeromorphicOn (Blaschke R w) Set.univ := by
-  intro x hx
-  unfold Blaschke
-  fun_prop
-
-lemma analyticOnNhd_blaschke (R : ℝ) (w : ℂ) (h : 0 < R) :
-    AnalyticOnNhd ℂ (Blaschke R w) {w}ᶜ := by
-  intro x hx
-  have : ↑R * (x - w) ≠ 0 := mul_ne_zero (ne_zero_of_re_pos h) (sub_ne_zero_of_ne hx)
-  unfold Blaschke
-  fun_prop (disch := aesop)
-
-lemma nonzero_blaschke {z : ℂ} (R : ℝ) (w : ℂ) (h : 0 < R) (hz : z ≠ w) (h₁ : ‖w‖ ≤ R) (h₂ : ‖z‖ ≤ R) :
-    Blaschke R w z ≠ 0 := by
-  -- Since $z \neq w$, the denominator $R(z - w)$ is non-zero. Also, from the given conditions, we know that $R^2 - \overline{w}z$ is not zero because if it were, then $\overline{w}z$ would equal $R^2$, which can't happen given the norms.
-  have h_denom_ne_zero : R * (z - w) ≠ 0 := by
-    exact mul_ne_zero ( Complex.ofReal_ne_zero.mpr h.ne' ) ( sub_ne_zero.mpr hz );
-  -- Since $z \neq w$, the denominator $R(z - w)$ is non-zero. Also, from the given conditions, we know that $R^2 - \overline{w}z$ is not zero because if it were, then $\overline{w}z$ would equal $R^2$, which can't happen given the norms. Hence, $Blaschke R w z \neq 0$.
-  have h_num_ne_zero : R^2 - (conj w) * z ≠ 0 := by
-    contrapose! h_denom_ne_zero; simp_all +decide [ Complex.ext_iff, sq ] ;
-    norm_num [ Complex.normSq, Complex.norm_def ] at *;
-    rw [ Real.sqrt_le_iff ] at *;
-    exact Or.inr ⟨ by nlinarith [ sq_nonneg ( w.re - z.re ), sq_nonneg ( w.im - z.im ) ], by nlinarith [ sq_nonneg ( w.re - z.re ), sq_nonneg ( w.im - z.im ) ] ⟩;
-  exact div_ne_zero h_num_ne_zero h_denom_ne_zero
-
-lemma xx (R : ℝ) (w : ℂ) :
-    MeromorphicAt (Blaschke R w) w := meromorphicOn_blaschke R w w (Set.mem_univ w)
-
-lemma order_blaschke (R : ℝ) (w : ℂ) (h : 0 < R) (h₂ : ‖w‖ ≠ R) :
-    (xx R w).order = -1 := by
-  unfold Blaschke
-  rw [MeromorphicAt.order_mul]
+-- Use the theorem on dominated convergence to show the following formula for
+-- integrals. Show that for ρ sufficiently close to R, the norm of the integrand
+-- '((herglotzRieszKernel 0 w (circleMap 0 ρ θ)).re * Real.log ‖circleMap 0 ρ θ - w‖)'
+-- is bounded by a constant times
+-- '((herglotzRieszKernel 0 w (circleMap 0 R θ)).re * Real.log ‖circleMap 0 R θ - w‖)'
+-- and this is integrable.
+theorem test (hw : ‖w‖ < R) (hp : ‖p‖ = 1) :
+    ∀ ρ ∈ Set.Ioo ‖w‖ R,
+    ∫ θ : ℝ in (0)..2 * π, ((herglotzRieszKernel 0 w (circleMap 0 ρ θ)).re * Real.log ‖circleMap 0 ρ θ - w‖) = 0
+    → ∫ θ : ℝ in (0)..2 * π, ((herglotzRieszKernel 0 w (circleMap 0 R θ)).re * Real.log ‖circleMap 0 R θ - w‖) = 0 := by
   sorry
-
-lemma meromorphicNFOn_blaschke (R : ℝ) (w : ℂ) (h : 0 < R) :
-    MeromorphicNFOn (Blaschke R w) Set.univ := by
-  intro z hz
-  unfold Blaschke
-  by_cases h₁ : z = w
-  · rw [meromorphicNFAt_iff_analyticAt_or]
-    right
-    use (meromorphicOn_blaschke R w z (Set.mem_univ z))
-    constructor
-    · simp_all only [Set.mem_univ, order_blaschke R w h]
-      exact sign_eq_neg_one_iff.mp rfl
-    simp_all
-  apply (analyticOnNhd_blaschke R w h z h₁).meromorphicNFAt
-
-lemma blaschke_eval_center (R : ℝ) (w : ℂ) :
-    Blaschke R w w = 0 := by
-  simp [Blaschke]
-
-lemma blaschke_eval_circle_ne {z : ℂ} (R : ℝ) (w : ℂ) (h : 0 < R) (h₂ : ‖z‖ = R) (h₃ : z ≠ w) :
-    ‖Blaschke R w z‖ = 1 := by
-  -- By definition of Blaschke factor, we have ‖Blaschke R w z‖ = ‖(R² - conj w * z) / (R * (z - w))‖.
-  simp [Blaschke];
-  rw [ div_eq_iff ] <;> simp_all +decide [ Complex.normSq, Complex.norm_def ];
-  · rw [ ← Real.sqrt_sq_eq_abs ];
-    rw [ ← Real.sqrt_mul <| by positivity ]
-    congr 1
-    norm_cast
-    rw [ ← h₂ ]
-    rw [ Real.sq_sqrt <| by nlinarith ]
-    ring;
-  · exact ⟨ h.ne', ne_of_gt <| Real.sqrt_pos.mpr <| not_le.mp fun h' => h₃ <| by refine' Complex.ext _ _ <;> nlinarith ⟩
-
-lemma log_blaschke_eval_circle {z : ℂ} (R : ℝ) (w : ℂ) (h : 0 < R) (h₂ : ‖z‖ = R) (h₃ : z ≠ w) :
-    Real.log ‖Blaschke R w z‖ = 0 := by
-  by_cases hz : z = w
-  all_goals simp_all [blaschke_eval_circle_ne]