Recursive decomposition coefficient inequality for real-rooted f-polynomials

Let f(t)=1+i=1dfi1tiN[t]f(t)=1+\displaystyle{\sum_{i=1}^d} f_{i-1}t^i\in\mathbb{N}[t] be a polynomial whose zeros are all real. Suppose that its recursive decomposition is f(t)=g(t)+th(t)f(t)=g(t)+th(t), where

g(t)=1+i=1dgiti,h(t)=1+i=1d1hiti.g(t)=1+\displaystyle{\sum_{i=1}^d}g_it^i,\qquad h(t)=1+\displaystyle{\sum_{i=1}^{d-1}}h_it^i.

Recursive decomposition inequality. For every relevant index ii, one has higih_i\leq g_i.

The recursive decomposition arises from the binomial expansions of the coefficients of an ff-polynomial and is intended to yield a positive answer to the question referenced in the source. The supplied text does not state whether this conjecture has been resolved.

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Primary source

Lili Mu and Volkmar Welker, “On a question about real rooted polynomials and f-polynomials of simplicial complexes”, arXiv:2503.24076 (2025).

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