Integral-group and Ehrhart characterization conjecture for uniform clutters

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Let C\mathcal C be a uniform clutter with edge incidence vectors v1,…,vqv_1,\ldots,v_q, and suppose its packing property holds. Define

B=((v1,1),…,(vq,1))B=((v_1,1),\ldots,(v_q,1))

as the matrix whose columns are the augmented vectors, let rr be the rank of BB, let Δr(B)\Delta_r(B) be the corresponding determinantal divisor, and set

P=conv⁡(v1,…,vq).P=\operatorname{conv}(v_1,\ldots,v_q).

Here K[Ft]‾\overline{K[Ft]} is the integral closure of the homogeneous ring K[Ft]K[Ft], and A(P)A(P) is the Ehrhart ring of PP. Integral-group and Ehrhart characterization conjecture. If C\mathcal C is a uniform clutter with the packing property, then all of the following equivalent conditions hold: (a) Zn+1/((v1,1),…,(vq,1))\mathbb{Z}^{n+1}/((v_1,1),\ldots,(v_q,1)) is a free group; (b) Δr(B)=1\Delta_r(B)=1; (c) BB diagonalizes over Z\mathbb{Z} to an identity matrix; and (d) K[Ft]‾=A(P)\overline{K[Ft]}=A(P). The source presents this as a consequence suggested by the preceding conjecture, but gives no resolution status.

References

Primary source

Luis A. Dupont and Rafael H. Villarreal, “Algebraic and combinatorial properties of ideals and algebras of uniform clutters of TDI systems”, arXiv:0801.1478 (2009).

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