OpenAI reports the Harary–Hill crossing-number formula

For every n≥3, the ordinary crossing number of Kₙ equals ¼⌊n/2⌋⌊(n−1)/2⌋⌊(n−2)/2⌋⌊(n−3)/2⌋.

Sources for this record

What was already known

The conjectured value was known as an upper bound, with exact small cases and weaker general lower bounds; the manuscript cites semidefinite estimates and restricted drawing classes.

AI involvement AI-led

OpenAI credits itself as manuscript author and states that its internal frontier model produced the results in this release. Individual human input is not detailed enough to establish task-only autonomy.

OpenAI is named as author on the manuscript, and its release attributes the results to an internal frontier model. The individual human input is not detailed enough to establish autonomy.

Importance Major

Resolves the Harary–Hill conjecture for complete graphs of every order.

Limitations

The formalized crossing count uses spatial crossing points, including repeated crossings of one edge pair; n=1,2 are trivial zero cases outside the selected n≥3 statement.

Technical verification Formal (Lean 4)

OpenAI reports a Lean proof matching the selected claim.

Formal checking

The pinned OpenAI Lean scope note identifies this selected claim.

Checker
OpenAI-reported Lean 4 / Comparator
Scope
For every n≥3, the ordinary crossing number of Kₙ equals ¼⌊n/2⌋⌊(n−1)/2⌋⌊(n−2)/2⌋⌊(n−3)/2⌋.
Basis
Reported by the linked checker
Evidence source

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

Human understanding Few

Few is the default when evidence for a higher level is insufficient. No named person is documented as explaining the central argument for this assessed contribution.

Correction and publication history

2026-10-18 · publication

Primary manuscript, attribution, prior-work, and scoped checking review for non-notifying local inclusion.

Read this published revision