PPL 147 / 177 permanent IDsPrize Problem Ledger · PPLChecked 2026.07.26
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Prize Problem LedgerIndependentPPL 147Shallit #15 · NFA length-universality complexity

Permanent problem IDPPL 147

Source-statedIndependentconjecture

Formal languages

Shallit #15 · NFA length-universality complexity

Given an NFA, decide whether it accepts every word of some length. The problem is PSPACE-hard; is it in PSPACE?

automata theorytheoretical computer scienceformal languages
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The problem

Given an NFA, decide whether it accepts every word of some length. The problem is PSPACE-hard; is it in PSPACE?

Open since2012historical source
Last checked2026.07.26Catalog verification
02

Reward offers

Offer 01£25Jeffrey Shallit
Personal offer

Personal cash offer stated in Shallit’s official talk. The live talks page records subsequent updates, including a paid solution to one omitted problem; confirm claim procedure with the sponsor before relying on the award.

Award source ↗Rules ↗
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Sources & reading

2 unique reference linksSponsor’s official problem slides Claim or award rules
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Related open targets

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