Two roots in one lemniscate component force a critical point
ProvedErdos1041.Counterexample.s2_two_zeros_gives_critical_pointdegree-seven-counterexampleerdos-1041polynomial-lemniscate
For a positive-degree complex polynomial p, if two distinct roots lie in one connected component of its strict unit lemniscate, that component contains a zero of p’s derivative.
Preamble
import Definitions.Def_ErdosProblems_Erdos1041_Counterexample_Defs import Mathlib import Mathlib.Algebra.Polynomial.Derivative import Mathlib.Algebra.Polynomial.Div import Mathlib.Algebra.Polynomial.Roots import Mathlib.Analysis.SpecialFunctions.Complex.Log import Mathlib.Analysis.SpecialFunctions.Pow.Real import Mathlib.Analysis.SpecialFunctions.Trigonometric.Basic import Mathlib.Tactic.NormNum import Mathlib.Tactic.Ring import Mathlib.Topology.Connected.LocallyConnected import Mathlib.Topology.EMetricSpace.BoundedVariation /-! External source: ani, erdosproblems.com forum thread 1041, 7 Sept 2026. Formalisation of Lemma 2.1 from `ani_degree7_counterexample.tex`. -/ /- Integration: move the S2 declaration out of Defs before importing this module. The supplied Defs is preserved under input/; see DEFS_DELTAS.md. Repaired and compiled against Mathlib v4.29.1 (commit 5e932f97). -/ noncomputable section open Set Filter Topology open Erdos1041.Counterexample
Formal statement
theorem Erdos1041.Counterexample.s2_two_zeros_gives_critical_point
(p : Polynomial ℂ) (hp : 0 < p.natDegree) (z : ℂ) (hz : z ∈ Omega p)
(w₁ w₂ : ℂ) (hw₁ : w₁ ∈ connectedComponentIn (Omega p) z)
(hw₂ : w₂ ∈ connectedComponentIn (Omega p) z) (hne : w₁ ≠ w₂)
(hr₁ : p.IsRoot w₁) (hr₂ : p.IsRoot w₂) :
∃ cc ∈ connectedComponentIn (Omega p) z, (Polynomial.derivative p).IsRoot cc := by sorry
Source
Lean source: https://github.com/wcook04/plectis-erdos-lean/blob/cc7e541cf2081c6fef5a5e377d52e365e33b01eb/ErdosProblems/Erdos1041/Counterexample/Components.lean#L225-L296
Construction by ani: https://www.erdosproblems.com/forum/thread/1041#post-8861
Related paper and provenance: https://github.com/wcook04/plectis-erdos/blob/551bae6dc6e732cf85172d66323c8d2bc77ba962/paper/1041/erdos-1041-lemniscate-newton-flow.tex#L25-L99
Paper prior-art bibliography: https://github.com/wcook04/plectis-erdos/blob/551bae6dc6e732cf85172d66323c8d2bc77ba962/paper/1041/erdos-1041-lemniscate-newton-flow.tex#L1662-L1772
AI-assisted formalization in Will Cook's project; ani is credited for the degree-seven construction. Independent correspondence of the 1958 Problem 5 wording to this modern formulation is unrecorded.