Optimal packings of one to seven unit squares in a disk

The-Anh Vu-Le

For five, six and seven freely rotated, interior-disjoint unit squares in a closed disk, the project reports exact least radii √(5/2), √q* and √13/2, respectively, where q* is its specified quartic root. It classifies all optimal packings up to rotation and relabelling: the five- and six-square optima are unique, while seven squares admit a three-parameter family.

Sources for this record

What was already known

Earlier packing catalogs listed candidate arrangements for these cases without cited optimality proofs. Results for one to four squares are separate claims.

AI involvement AI-led

The project credits ChatGPT with the n=5 and n=7 proofs and the analytical n=6 proof, with Claude models supplying the occupied-arc idea, certificates and formalization support. The-Anh Vu-Le directed and reviewed the statements.

The source assigns the central proofs and six-square certificate-to-analysis step to the models; the owner set scope and reviewed statements.

Importance Notable

Establishes exact optimality and classification for three previously open small packing cases.

Limitations

The reported Lean checking covers the n=5,6,7 radii and classifications. The n=3 exactness claim and n=4 priority overlap are outside this assessment. No independent human mathematical review is documented.

Technical verification Formal (Lean 4/Mathlib, Comparator, NanoDa and con-ron)

The source reports sorry-free Lean proofs of the exact radii and optimal-packing classifications, Comparator statement comparison, and independent kernel replay.

Formal checking

Repository reports sorry-free Lean proofs and statement comparison for the selected cases.

Checker
Lean 4 kernel and reported Comparator replay
Scope
SquaresInCircles.optimal_radius and optimal_packings for n=5,6,7
Basis
Reported by the linked checker
Evidence source

Checking a formal statement does not establish that it matches the original problem.

Human understanding Few

The owner reviewed the statement and documentation, but no person's explanation of the central arc and six-square separation proofs is identified; this is the evidence-gap default.

Correction and publication history

2026-10-18 · publication

The reported Lean proofs cover optimal radii and classifications for five, six and seven squares.

Read this published revision