Close pair among three equidistant points of a thin annulus, all radii
ProvedEsgk.scaled_annular_equidistant_triple_close_pair_sharpdiscrete-geometrygeometry
Let , let , and let be real numbers with , and
Assume that , that each lies in the closed annulus
and that are equidistant from , that is for all . Then there are indices with
No bound on the common distance is assumed, and for only the lower annulus bound is assumed. The points need not be distinct.
For small the admissible threshold is close to : three points of a thin annulus on any circle about such a point contain a pair at squared distance about . It is the all-radius counterpart of the close-pair statement for circles of radius at most .
Formalization Note Points are elements of EuclideanSpace ℝ (Fin 2), the triple is a function Fin 3 → ℝ², and all thresholds are stated for squared distances.
Preamble
/- Copyright (c) 2026 Adam McKenna. All rights reserved. Released under Apache 2.0 license as described in the file LICENSE. Authors: Adam McKenna -/ import Definitions.Def_Esgk_Foundation open EuclideanGeometry Esgk
Formal statement
namespace Esgk
theorem scaled_annular_equidistant_triple_close_pair_sharp
(c p : Point) (q : Fin 3 → Point) {ρ x σ t : ℝ} (hρ : 0 < ρ)
(hσ : 0 < σ) (hσx : σ ^ 2 ≤ 1 - x) (ht : x * (σ + 1) ≤ σ * t)
(hp : ρ ^ 2 * (1 - x) ≤ dist p c ^ 2)
(hlo : ∀ i, ρ ^ 2 * (1 - x) ≤ dist (q i) c ^ 2)
(hhi : ∀ i, dist (q i) c ^ 2 ≤ ρ ^ 2)
(heq : ∀ i j, dist p (q i) = dist p (q j)) :
∃ i j : Fin 3, i ≠ j ∧ dist (q i) (q j) ^ 2 ≤ t * ρ ^ 2 := by sorry
end EsgkSource
Lean formalization by Adam McKenna (2026), declaration Esgk.scaled_annular_equidistant_triple_close_pair_sharp.