An exponential two-way deterministic state lower bound for one-way liveness

OpenAI

For each h≥2, an h+3-state one-way nondeterministic automaton recognizes liveness of products of binary relations, while every equivalent two-way deterministic automaton with s states satisfies 2^⌊(h−2)/31⌋≤4(s+2)². The finite alphabet grows with h.

Sources for this record

What was already known

The Sakoda–Sipser question asks the state cost of removing nondeterminism in two-way automata. The cited unrestricted deterministic lower bound for the growing-alphabet liveness family was quadratic.

AI involvement AI-led

OpenAI credits its internal model with the manuscript and proof artifacts; item-specific autonomy is not documented.

OpenAI is the credited author and the release says its internal model produced the mathematical manuscripts; item-specific independence is undocumented.

Importance Major

Rules out an alphabet-independent polynomial simulation bound for this one-way family.

Limitations

The result concerns growing alphabets and does not settle fixed-alphabet variants. The source-reported Lean proof was not independently rebuilt.

Technical verification Formal (Lean 4 formalization with OneWayLiveness Comparator)

The released scope note states the liveness lower bound and links a matching Lean Comparator target. The formalization concerns growing alphabets and both acceptance conventions, with one sharper factor. The source reports a machine formalization.

Formal checking

Exponential two-way deterministic state lower bound for the h+3-state one-way liveness family over growing alphabets. Formal proof with scope note and OneWayLiveness Comparator statement

Checker
Lean 4 formal development in the OpenAI math release
Scope
Exponential two-way deterministic state lower bound for the h+3-state one-way liveness family over growing alphabets
Basis
Reported by the linked checker
Evidence source

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

Human understanding Few

No named human explanation of the central lower-bound mechanism was found in the released release; Few is the evidence default.

Correction and publication history