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Williams's one-tape question: simulating one-tape time TT in O(T1/2−δ)O(T^{1/2-\delta}) space

Theorem 1.1: for a fixed deterministic machine with one writable tape and head (and finitely many read-only input heads), the finite-control and halting outcome by time TT can be computed in O(T2/5log⁡C(T+2))O(T^{2/5}\log^C(T+2)) work-space bits given the cap TT; without a supplied cap, a machine halting at time tt is simulated in O((t+2)2/5 polylog)O((t+2)^{2/5}\,\mathrm{polylog}) space. Hence O(T1/2−δ)O(T^{1/2-\delta}) for every δ<1/10\delta<1/10. Simulation time is unrestricted, the final tape is not materialized, no lower bound or optimality is claimed, and for several writable tapes only O(T polylog)O(\sqrt T\,\mathrm{polylog}) is given.

Exact FrontierDelta

Prior state unknown→proved

Scope and record

Occurred: Sep 25, 2026

Delta type: SOURCE CLAIM

Assumptions: VibeMathed verification: lean-checked. Publication: announcement. AI contribution: ai-discovered. VibeMathed editorial classifications, scores, notes, relations, and dataset structure are CC BY 4.0. Source statements and linked content retain their own rights.

Canonical aliases: Williams's one-tape question: simulating one-tape time $T$ in $O(T^{1/2-\delta})$ space · One-tape time in sub-square-root space

Confidence: Not scored

Registry verification: lean checked · announcement · candidate

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Attribution

VibeMathed
registry · event recorded by

Unreleased internal OpenAI model
model · ai model contributor · OpenAI

Artifacts and verifiers

Lean Comparator challenge OneTapeSpace (OpenAI math release)

lean artifact · pending

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Compute record

No linked compute attempts recorded.

Lineage and corrections

This event attributed to Unreleased internal OpenAI model

Theorem 1.1: for a fixed deterministic machine with one writable tape and head (and finitely many read-only input heads), the finite-control and halting outcome by time TT can be computed in O(T2/5log⁡C(T+2))O(T^{2/5}\log^C(T+2)) work-space bits given the cap TT; without a supplied cap, a machine halting at time tt is simulated in O((t+2)2/5 polylog)O((t+2)^{2/5}\,\mathrm{polylog}) space. Hence O(T1/2−δ)O(T^{1/2-\delta}) for every δ<1/10\delta<1/10. Simulation time is unrestricted, the final tape is not materialized, no lower bound or optimality is claimed, and for several writable tapes only O(T polylog)O(\sqrt T\,\mathrm{polylog}) is given. parent of this event

Lean Comparator challenge OneTapeSpace (OpenAI math release) evidence for this event

Williams, Simulating Time with Square-Root Space (full version, Section 5) evidence for this event

Williams's one-tape question: simulating one-tape time TT in O(T1/2−δ)O(T^{1/2-\delta}) space parent of this event

VibeMathed record: Williams's one-tape question: simulating one-tape time TT in O(T1/2−δ)O(T^{1/2-\delta}) space evidence for this event

Williams's one-tape question: simulating one-tape time TT in O(T1/2−δ)O(T^{1/2-\delta}) space evidence for this event

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