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Six-core rigidity for the n=7 canonical configuration

Proved
CirclePackingConstants.n7_six_core_rigidity

by xuanji · Sep 27, 2026 · Mathlib 0df444a (Lean v4.33.1)

circle-packingn7rigidity

The bounded signed displacement system and its eight contact inequalities force all twelve core displacements to vanish.

Preamble
import Mathlib.Data.Real.Basic
import Mathlib.Tactic.Linarith
import Mathlib.Tactic.NormNum
import Mathlib.Tactic.Ring
import Mathlib.Tactic.FieldSimp
import Mathlib.Tactic.Positivity
Formal statement
theorem CirclePackingConstants.n7_six_core_rigidity
    (s r M eta : ℝ)
    (a b c e f g h i j k l t : ℝ)
    (hs : 0 < s)
    (hs_half : (1 : ℝ) / 2 < s)
    (hr0 : 0 ≤ r)
    (hr15 : (3 : ℝ) / 2 ≤ r)
    (hr18 : r ≤ (9 : ℝ) / 5)
    (hr2 : r ^ 2 = 3)
    (hrel : 2 * (1 - s) = r * s)
    (hM0 : 0 ≤ M)
    (hMsmall : M ≤ (1 : ℝ) / 100)
    (heta : eta = 4 * M ^ 2 / s)
    (hmax : M = max (|a|) (max (|b|) (max (|c|) (max (|e|) (max (|f|) (max (|g|)
      (max (|h|) (max (|i|) (max (|j|) (max (|k|) (max (|l|) (|t|))))))))))))
    (haL : -M ≤ a) (haU : a ≤ M)
    (hbL : -M ≤ b) (hbU : b ≤ M)
    (hcL : -M ≤ c) (hcU : c ≤ M)
    (heL : -M ≤ e) (heU : e ≤ M)
    (hfL : -M ≤ f) (hfU : f ≤ M)
    (hgL : -M ≤ g) (hgU : g ≤ M)
    (hhL : -M ≤ h) (hhU : h ≤ M)
    (hiL : -M ≤ i) (hiU : i ≤ M)
    (hjL : -M ≤ j) (hjU : j ≤ M)
    (hkL : -M ≤ k) (hkU : k ≤ M)
    (hlL : -M ≤ l) (hlU : l ≤ M)
    (htL : -M ≤ t) (htU : t ≤ M)
    (hwa : 0 ≤ a) (hwb : 0 ≤ b) (hwe : 0 ≤ e) (hwh : 0 ≤ h)
    (hwf : f ≤ 0) (hwt : t ≤ 0)
    (C1 : s ^ 2 ≤ (s + c - a) ^ 2 + (e - b) ^ 2)
    (C2 : s ^ 2 ≤ (h - a) ^ 2 + (s + i - b) ^ 2)
    (C3 : s ^ 2 ≤ (j - c) ^ 2 + (s + k - e) ^ 2)
    (C4 : s ^ 2 ≤ (s + j - h) ^ 2 + (k - i) ^ 2)
    (C5 : s ^ 2 ≤ (1 - s + f - c) ^ 2 + (s / 2 + g - e) ^ 2)
    (C6 : s ^ 2 ≤ (1 - s + f - j) ^ 2 + (-s / 2 + g - k) ^ 2)
    (C7 : s ^ 2 ≤ (s / 2 + l - h) ^ 2 + (1 - s + t - i) ^ 2)
    (C8 : s ^ 2 ≤ (-s / 2 + l - j) ^ 2 + (1 - s + t - k) ^ 2) :
    a = 0 ∧ b = 0 ∧ c = 0 ∧ e = 0 ∧ f = 0 ∧ g = 0 ∧
      h = 0 ∧ i = 0 ∧ j = 0 ∧ k = 0 ∧ l = 0 ∧ t = 0  := by sorry
Source
Supplied circles_in_square_n7.pdf, §2 (six-core rigidity) and Appendix A.

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