AI-assisted certificate reports optimality of logarithmic-spiral shoreline search

Alexander Temerev reports that every planar search path for an unknown straight shoreline has competitive ratio at least 13.8111351794611…, matching the logarithmic spiral. The proof permits paths with decreasing radius or reversing polar angle.

Sources for this record

What was already known

The logarithmic spiral was conjectured optimal by Baeza-Yates, Culberson and Rawlins. Previous general lower bounds and stronger bounds under cyclic restrictions did not establish unrestricted optimality.

AI involvement AI-centered

GPT-6 Astra, Claude Fable 5.1 and Claude Opus 5 helped find the reduction and storage function and write Lean modules and two interval-arithmetic verifiers. Humans directed the work and the manuscript documents audit-driven repairs.

Temerev credits GPT-6 Astra, Claude Fable 5.1 and Claude Opus 5 with finding the reduction and storage function, with human direction and audit-driven repairs.

Importance Notable

Reports a matching unrestricted minimax bound for a longstanding geometric online-search problem.

Limitations

The reported Lean proofs cover specified reduction lemmas, and two Arb interval implementations check the certificate inequalities. Section 10 lists geometric and measure-theoretic steps outside the Lean formalization. The broader proof remains a source-reported result.

Technical verification Partial

Section 10 reports Lean checks of selected lemmas and two Arb interval checks of the certificate. It expressly lists geometric and measure-theoretic steps not formalized, so the full theorem is not machine checked.

Formal checking

The author reports zero-sorry Lean checks of listed lemmas and two Arb interval certificate checks; Section 10 lists the unformalized steps.

Checker
Author-reported Lean 4 and Arb checkers
Scope
Selected polygonal, angular and bookkeeping lemmas plus the storage-function inequalities, not the full geometric reduction.
Basis
Reported by the linked checker
Evidence source

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

Human understanding Full

Temerev gives a detailed human-written outline and prose derivation of the reduction, control problem and storage-function certificate, documenting the central reasoning.

Correction and publication history

2026-10-18 · publication

Primary-source review under the four independent curation dimensions. This restores the original archived contribution identity without subscriber notification.

Read this published revision