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Resilience forces large disjoint packings of violating proper witnesses: 256k(k−1)∣P∣>N256k(k-1)|\mathcal P|>N256k(k−1)∣P∣>N (29) (Erdős 624)

Proved
Erdos624.resilient_packing_bound

by Ethan Cheung · Oct 24, 2026 · Mathlib 0df444a (Lean v4.33.1)

combinatoricserdos-problems

Let UUU be a finite set, CCC a finite set of colours, g0,g1:P(U)→Cg_0,g_1:\mathcal P(U)\to Cg0​,g1​:P(U)→C, L(A)={g0(A),g1(A)}L(A)=\{g_0(A),g_1(A)\}L(A)={g0​(A),g1​(A)}, V⊆UV\subseteq UV⊆U with N=∣V∣N=|V|N=∣V∣, k∈Nk\in\mathbb Nk∈N and u∈Cu\in Cu∈C. The proper minimal witnesses of a colour uuu inside WWW are the A⊆WA\subseteq WA⊆W with 0<∣A∣<k0<|A|<k0<∣A∣<k, u∈L(A)u\in L(A)u∈L(A) and u∉L(B)u\notin L(B)u∈/L(B) for all B⊊AB\subsetneq AB⊊A; a certificate is w:U→F2w:U\to\mathbf F_2w:U→F2​ with ∑x∈Aw(x)=1\sum_{x\in A}w(x)=1∑x∈A​w(x)=1 on every such AAA. Assume uuu is resilient: for every R⊆VR\subseteq VR⊆V with 256k∣R∣≤N256k|R|\le N256k∣R∣≤N, the proper minimal witnesses of uuu in V∖RV\setminus RV∖R admit no certificate. Then for every form w:U→F2w:U\to\mathbf F_2w:U→F2​ there is a family P\mathcal PP of pairwise disjoint proper minimal witnesses A⊆VA\subseteq VA⊆V of uuu with ∑x∈Aw(x)=0\sum_{x\in A}w(x)=0∑x∈A​w(x)=0 and

N<256k(k−1)∣P∣.(29)N<256k(k-1)|\mathcal P|.\qquad(29)N<256k(k−1)∣P∣.(29)

(Here k−1k-1k−1 is truncated natural-number subtraction; no lower bound on kkk is needed.)

Context: Erdős Problem 624 asks whether H(n)−log⁡2n→∞H(n)-\log_2 n\to\inftyH(n)−log2​n→∞, where H(n)H(n)H(n) is the least mmm such that some f:P(X)→Xf:\mathcal P(X)\to Xf:P(X)→X with ∣X∣=n|X|=n∣X∣=n satisfies f[P(Y)]=Xf[\mathcal P(Y)]=Xf[P(Y)]=X for all ∣Y∣≥m|Y|\ge m∣Y∣≥m. This is an auxiliary finite statement from Sol's Round 12 Step 17 cross-review / resilience analysis of the two-track (PAIR) case. It does not settle Erdős Problem 624, PAIR or Step 17.

Preamble
import Mathlib
open Finset
Formal statement
namespace Erdos624

theorem resilient_packing_bound {U : Type*} [Fintype U] [DecidableEq U]
    {C : Type*} [Fintype C] [DecidableEq C] (k : ℕ) (g0 g1 : Finset U → C) (V : Finset U) (u : C)
    (hres : ∀ R ⊆ V, 256 * k * #R ≤ #V → ¬ ∃ w : U → ZMod 2, ∀ A ⊆ V \ R, 0 < #A → #A < k →
        u ∈ ({g0 A, g1 A} : Finset C) → (∀ B ⊂ A, u ∉ ({g0 B, g1 B} : Finset C)) →
          ∑ x ∈ A, w x = 1)
    (w : U → ZMod 2) :
    ∃ P : Finset (Finset U),
      (∀ A ∈ P, A ⊆ V ∧ 0 < #A ∧ #A < k ∧ u ∈ ({g0 A, g1 A} : Finset C) ∧
        (∀ B ⊂ A, u ∉ ({g0 B, g1 B} : Finset C)) ∧ ∑ x ∈ A, w x = 0) ∧
      (∀ A ∈ P, ∀ B ∈ P, A ≠ B → Disjoint A B) ∧
      #V < 256 * k * (k - 1) * #P := by sorry

end Erdos624
Source
Erdős Problem 624 (https://www.erdosproblems.com/624); Round 12: Sol's 'Step 17: First-Round Cross-Review' and 'Step 17: resilient relations below the top layer'; derived from GPT 6.1 Sol's analysis, relayed by Ethan Cheung; hand-checked and Lean-verified by Grok Bot for Ethan Cheung (Oct 24 2026). Auxiliary result only; does NOT settle PAIR / Step 17 / #624.

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