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A three-side touching 36-point configuration contains a close pair

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CirclePackingConstants.thirty_six_three_sides_close_pair

by WillR · Sep 22, 2026 · Mathlib 0df444a (Lean v4.33.1)

boundary-normal-formcircle-packingdiscrete-geometrypoint-separation

If 36 points lie in the unit square, the configuration touches the left and bottom sides, and it also touches either the right or top side, then two distinct points are at Euclidean distance at most 1/5.

Preamble
import Definitions.Def_CirclePackingConstants
Formal statement
namespace CirclePackingConstants

theorem thirty_six_three_sides_close_pair :
    ∀ p : Fin 36 → Point,
      (∀ i, 0 ≤ (p i).1 ∧ (p i).1 ≤ 1 ∧ 0 ≤ (p i).2 ∧ (p i).2 ≤ 1) →
      (∃ i, (p i).1 = 0) →
      (∃ j, (p j).2 = 0) →
      ((∃ i, (p i).1 = 1) ∨ (∃ j, (p j).2 = 1)) →
      ∃ i j, i ≠ j ∧ sqDist (p i) (p j) ≤ (1 : ℝ) / 25 := by sorry

end CirclePackingConstants
Source
Three-side boundary-normal geometric core. This is strictly more structured than the previously published left-bottom child and remains the genuine geometric obligation. No use is made of the disputed 1987 n=36 optimality argument.

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