Hankel total positivity conjecture for vincular pattern Classes 1 and 2

For each n0n\geq 0, let Pn(1)(x)P_n^{(1)}(x) and Pn(2)(x)P_n^{(2)}(x) be the generating polynomials for the number of occurrences of vincular patterns in Class 11 and Class 22, respectively. A polynomial sequence is coefficientwise Hankel totally positive in xx when every minor of its Hankel matrix has coefficients that are nonnegative polynomials in xx.

Hankel total positivity conjecture. The sequences of polynomials

(Pn(1)(x+1))n0,(Pn(2)(x+1))n0\left(P_n^{(1)}(x+1)\right)_{n\geq 0},\qquad \left(P_n^{(2)}(x+1)\right)_{n\geq 0}

are both coefficientwise Hankel totally positive with respect to the variable xx.

The unshifted sequences are not coefficientwise Hankel totally positive, while computations suggest that the shift xx+1x\mapsto x+1 restores this stronger positivity property. The claim is supported by finite tests but remains open.

Sources & referencesView supporting material

Primary source

Bishal Deb, “Cyclic sieving phenomena via combinatorics of continued fractions”, arXiv:2508.13709 (2025).

Additional references

5 papers in this index state this conjecture (2018–2025). The statement above is taken from the most recent of them; the others are arXiv:2507.18959, arXiv:2105.05583, arXiv:1807.01062, arXiv:1807.03271.

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