slug: archer-bourne-cube-2143-count
bibkey: archer2026pattern
doi: 10.46298/dmtcs.17199
triage: window
motivation_gids:
  - D5/S3/ConceptDynamics/PatternAvoidance/RotationSumPowerPatternAvoidance
  - D5/S3/ConceptDynamics/PatternAvoidance/ArcherBourneDecomposition

Archer-Bourne cube-avoidance counting equality

Problem

This dossier deliberately anchors only the unnumbered counting conjecture in Section 5, “Further directions and open questions”, page 13 of arXiv:2505.05218v3. The worker extracted this sentence from the PDF; line wrapping is removed and mathematical glyphs are transcribed into inline LaTeX:

For example, based on the ideas similar to the ones in this paper, we conjecture that the number of permutations that avoid the chain $(312,321:\varnothing :2143)$ (i.e, those with the property that $\pi$ avoids $\{312,321\}$ and ${\pi }^3$ avoids $2143$) is equal to the number of compositions $d=(d_1,d_2,\dots ,d_m)$ of $n$ so that all $d_i$ are 1 or 3, except for at most one.

Thus, for each positive n, count permutations of n avoiding 312 and 321 whose cubes avoid 2143, and compare with ordered compositions of n having at most one part outside {1,3}. The paper’s broader questions about other patterns and higher powers are deliberately out of scope.

Motivation

The frozen motivation module supplies an exact avoidance criterion for powers of direct sums of cyclic rotations. Its cube specialization provides the composition-side condition in the quoted conjecture. This is a concrete formal input to the counting bridge.

Gap

The formalization route is complete. Candidate theorem 6.222 supplies the decomposition, uniqueness of the indexing composition, and the restricted cardinality bijection needed to combine the earlier cube criterion with the published source results.

Route

The frozen half is rotationSumPerm_pow_avoids_2143_iff: for positive block sizes, the rth power of pi_d avoids 2143 exactly when at most one block size fails to divide r. Its frozen cube specialization, rotationSumPerm_cube_avoids_2143_iff, makes the exceptional sizes precisely those outside {1,3}.

The completed formal half is the decomposition of every 312/321-avoiding permutation as a direct sum of cyclic rotations, its bijectivity with compositions of n, and the restriction of that bijection to transport cardinalities using the cube criterion. Archer and Bourne already prove the decomposition in Lemma 3.1 on page 4 and identify the bijection on page 5; this part is formalization of a published result, not new mathematics. The worker read both passages in the fetched PDF.

card_avoids_312_321_cube_2143_eq_compositions combines the formalized bijection with the frozen criterion and proves the conjectured equality. Its Scribe declaration carries this problem’s Proved resolution claim. The decomposition and bijection retain literature provenance, while this final counting theorem is repository-derived.

Falsifier

A positive n with unequal exact counts on the two sides would refute the anchored conjecture. To validate a proposed enumeration, it must range over all permutations and all compositions of that n using the paper’s avoidance and composition conventions. No new enumeration was performed here. A formal bridge must preserve total size and prove both directions and uniqueness; the criterion for an already-given pi_d alone cannot certify those properties.

Evidence

• Frozen module: D5/S3/ConceptDynamics/PatternAvoidance/RotationSumPowerPatternAvoidance.lean.
• Public criterion theorems: rotationSumPerm_pow_avoids_2143_iff and rotationSumPerm_cube_avoids_2143_iff.
• Frozen bridge module: D5/S3/ConceptDynamics/PatternAvoidance/ArcherBourneDecomposition.lean.
• Public bridge and counting theorems: avoids_312_321_iff_exists_rotationSumComposition, rotationSumComposition_injective, and card_avoids_312_321_cube_2143_eq_compositions.
• Machine-checkable frozen-state receipt: Golden/Frozen/state/D5/S3/ConceptDynamics/PatternAvoidance/RotationSumPowerPatternAvoidance.lean.json. The worker’s test -f exited 0 on 2026-09-07.
• Library/Dynamics/archer2026pattern.md records the worker’s PDF fetch: HTTP 200, 374413 bytes, SHA-256 daec95fcbbf9b2c439b1a3680af97c01fe4912c1889fd312a0a8044ab6a497c9. The conjecture is on page 13; the published decomposition and bijection are on pages 4 and 5. Candidate 6.221 records the criterion, while 6.222 records the completed repository bridge; these numbers are provenance.

Triage

window. The repository route is complete: the decomposition and injectivity formalize the paper’s source results, and the final restricted cardinality bijection proves the anchored counting proposition. The final theorem carries the problem’s Proved resolution claim.

ASSUMED-UNVERIFIED

• No repository machine verifies that a Lean statement is equivalent to the paper’s natural-language proposition. This worker’s comparison of the extracted source with the Lean criterion, including rotations and avoidance conventions, is human reading evidence, not a proof of source-to-Lean equivalence.
• The decomposition and bijection are source results formalized in the repository. Their identification with the paper’s prose remains a reading comparison rather than a machine-verified translation.
• The API metadata and journal DOI redirect are caller-supplied readings dated 2026-09-07. The worker independently fetched and extracted the v3 PDF, but did not repeat those metadata requests.
• No literature search for a later resolution of the conjecture was performed. This dossier records only that arXiv:2505.05218v3 presents the statement as a conjecture; it does not assess the subsequent literature.