PPL 159 / 177 permanent IDsPrize Problem Ledger · PPLChecked 2026.07.26
Prize Problem LedgerIndependentPPL 159Shallit #9 · Nonzero Hankel determinants for a morphic word

Permanent problem IDPPL 159

Source-statedIndependentconjecture

Formal languages

Shallit #9 · Nonzero Hankel determinants for a morphic word

Does the fixed point generated by 1→12, 2→23, 3→14, 4→32 have all of its Hankel determinants nonzero?

automata theorytheoretical computer scienceformal languages
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The problem

Does the fixed point generated by 1→12, 2→23, 3→14, 4→32 have all of its Hankel determinants nonzero?

Open since2014source-stated by 2014
Last checked2026.07.26Catalog verification
02

Reward offers

Offer 01£50Jeffrey 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.

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Sources & reading