The quadratic critical value has two local preimages
ProvedErdos1041.Counterexample.bottleneck_two_local_preimagesdegree-seven-counterexampleerdos-1041polynomial-lemniscate
Under the source disk criterion and a sufficiently small nonzero η, p(cc)+aHat η² has two distinct preimages in cc’s lemniscate component, each within 5|η|/4 of cc.
Preamble
import Definitions.Def_ErdosProblems_Erdos1041_Counterexample_Defs import Definitions.Def_ErdosProblems_Erdos1041_Counterexample_Bottleneck 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 open Erdos1041 open Erdos1041.Counterexample noncomputable section open Topology open Erdos1041.Counterexample
Formal statement
theorem Erdos1041.Counterexample.bottleneck_two_local_preimages (p : Polynomial ℂ) (cc : ℂ)
(hcrit : (Polynomial.derivative p).IsRoot cc)
(aHat : ℂ) (haHat : aHat ≠ 0) (h s δ : ℝ) (hh : 0 < h) (hs : 0 < s)
(hsh : 5 / 4 * s < h) (hsδ : ‖aHat‖ * s ^ 2 ≤ δ) (hδ : δ = 1 - ‖p.eval cc‖)
(hdisk : ∀ z : ℂ, ‖z‖ ≤ h → ‖(shiftQuad p cc).eval z / aHat - 1‖ ≤ 1 / 4)
(η : ℂ) (hη : η ≠ 0) (hηs : ‖η‖ < s) :
∃ x₁ ∈ connectedComponentIn (Omega p) cc, ∃ x₂ ∈ connectedComponentIn (Omega p) cc,
x₁ ≠ x₂ ∧ p.eval x₁ = p.eval cc + aHat * η ^ 2 ∧
p.eval x₂ = p.eval cc + aHat * η ^ 2 ∧
‖x₁ - cc‖ ≤ 5 / 4 * ‖η‖ ∧ ‖x₂ - cc‖ ≤ 5 / 4 * ‖η‖ := by sorry
Source
Lean source: https://github.com/wcook04/plectis-erdos-lean/blob/cc7e541cf2081c6fef5a5e377d52e365e33b01eb/ErdosProblems/Erdos1041/Counterexample/Bottleneck.lean#L1304-L1351
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.