Palindromic decomposition conjecture for symmetric edge-polytope edge deletion

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Let GG be a 2-connected graph and let ijij be any edge of GG. Let Γ\Gamma be a unimodular triangulation of the subcomplex of PG∖ijP_{G\setminus ij} consisting of all facets visible by eije_{ij}. If the distinct lattice distances from eije_{ij} to facets of Γ\Gamma are h1>h2>⋯>hkh_1>h_2>\cdots>h_k, define

Γs:=⟨σ facet of Γ∣hσ≥hs⟩\Gamma_s:=\langle\sigma\text{ facet of }\Gamma\mid h_\sigma\ge h_s\rangle

for s=1,…,ks=1,\ldots,k, and set hΓ0(t):=0h_{\Gamma_0}(t):=0. Palindromic decomposition conjecture.

hPG∗(t)−hPG∖ij∗(t)=2t∑s=1k((hΓs(t)−hΓs−1(t))∑r=0hs−1tr).h^*_{P_G}(t)-h^*_{P_{G\setminus ij}}(t)=2t\sum_{s=1}^{k}\left(\left(h_{\Gamma_s}(t)-h_{\Gamma_{s-1}}(t)\right)\sum_{r=0}^{h_s-1}t^r\right).

Moreover, for every s=1,…,ks=1,\ldots,k, the polynomial

(hΓs(t)−hΓs−1(t))∑r=0hs−1tr\left(h_{\Gamma_s}(t)-h_{\Gamma_{s-1}}(t)\right)\sum_{r=0}^{h_s-1}t^r

is palindromic, has nonnegative coefficients, and has the same center as the left-hand side. This proposed formula would decompose the edge-deletion difference into palindromic pieces with nonnegative coefficients; the supplied text gives no resolution status.

References

Primary source

Giulia Codenotti, Roberto Riccardi and Lorenzo Venturello, “The number of edges of a symmetric edge polytope”, arXiv:2512.16572 (2026).

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