Shifted Hankel total positivity for bivariate forest polynomials

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Let fn,k♯(w)f^\sharp_{n,k}(w) and Fn♯(x,w)=∑k=0nfn,k♯(w)xkF_n^\sharp(x,w)=\sum_{k=0}^n f^\sharp_{n,k}(w)x^k be as above. A polynomial sequence is coefficientwise Hankel-totally positive when all minors of its Hankel matrix have coefficientwise nonnegative coefficients. Shifted bivariate-forest Hankel-total-positivity conjecture. (b) The sequence F♯=(Fn♯(x,−1+w′))n≥0{\bm{F}}^\sharp=\bigl(F_n^\sharp(x,-1+w')\bigr)_{n\geq 0} is coefficientwise Hankel-totally positive in x,w′x,w'. (c) The sequence F♯△=(fn+1,1♯(−1+w′))n≥0{\bm{F}}^{\sharp\triangle}=\bigl(f^\sharp_{n+1,1}(-1+w')\bigr)_{n\geq 0} is coefficientwise Hankel-totally positive in w′w'. These shifted claims are proposed after the corresponding matrix claim fails at order two; the source gives no resolution.

References

Primary source

Alan D. Sokal, “Total positivity of some polynomial matrices that enumerate labeled trees and forests, I. Forests of rooted labeled trees”, arXiv:2105.05583 (2022).

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