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Theoretical computer science

Exponential state costs for two-way automata

OpenAI research collection · 2 manuscripts · Source checked 2026-10-19

OpenAI's result summary

Proves exponential lower bounds both for complementing two-way nondeterministic finite automata and for simulating one-way nondeterministic automata by two-way deterministic ones. The latter resolves the Sakoda–Sipser state-succinctness conjecture over growing finite alphabets; both results rule out polynomial state bounds independent of alphabet size.

Read the manuscripts

Short excerpts below come from OpenAI's abstracts. The full abstract and original PDF preserve the paper's precise scope.

MANUSCRIPT 01

An exponential state lower bound for two-way nondeterministic complementation

We prove that two-way nondeterministic finite automata cannot be complemented with a polynomial number of states independent of the alphabet. For each n ≥ 4 we construct an n-state automaton over a finite alphabet whose complement requires at least \tfrac12 2^{\lfloor(n-4)/127\rfloor}-1 states.

This PDF is listed in OpenAI's formalization catalogue. See the scope and dependencies before interpreting coverage.

MANUSCRIPT 02

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

One-way liveness on h points accepts a word of binary relations when their ordered product is nonempty. For every h ≥ 2, it has a nondeterministic automaton with h+3 states and no left moves, whereas every equivalent s-state two-way deterministic automaton satisfies 4(s+2)^2\ge2^{\lfloor(h-2)/31\rfloor}. Partial transition…

Full source abstract

One-way liveness on h points accepts a word of binary relations when their ordered product is nonempty. For every h ≥ 2, it has a nondeterministic automaton with h+3 states and no left moves, whereas every equivalent s-state two-way deterministic automaton satisfies 4(s+2)^2\ge2^{\lfloor(h-2)/31\rfloor}. Partial transition rules, stay moves, and nonaccepting infinite computations are allowed. The alphabets are finite and grow with h, so the result rules out an alphabet-independent polynomial state bound for deterministic two-way simulation, already for one-way nondeterministic sources.

This PDF is listed in OpenAI's formalization catalogue. See the scope and dependencies before interpreting coverage.

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