OpenAI reports a two-fifths-power space simulation for one-tape machines

A fixed deterministic machine with one writable tape can be simulated through a supplied time cap T≥2 in O(T^(2/5) polylog(T+2)) work-space bits while preserving its finite-control and halting outcome.

Sources for this record

What was already known

The classical one-writable-tape simulation uses a square-root space exponent; Williams asked whether that exponent could be reduced by a fixed amount in this model.

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 Notable

Improves the one-tape time-to-space exponent from 1/2 to 2/5.

Limitations

The initial tape and read-only symbols must have fixed polylogarithmic-space access; the simulator’s running time is unrestricted, and the result does not cover general multitape machines.

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
A fixed deterministic machine with one writable tape can be simulated through a supplied time cap T≥2 in O(T^(2/5) polylog(T+2)) work-space bits while preserving its finite-control and halting outcome.
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