The converse Hasse–Witt rank conjecture for curves in characteristic 2

Let kk be a perfect field of characteristic 22, let Δ\Delta be a two-dimensional lattice polygon satisfying the conditions from Lemma~, and let ff be a Δ\Delta-non-degenerate (or Δ\Delta-toric) Laurent polynomial. Write CfC'_f for the associated curve, gg for its genus, and ρ\rho for the quantity defined in the preceding results. For each solution (i0,j0)ΔZ2(i_0,j_0)\in\Delta\cap\mathbf{Z}^2 of the system of congruences in, let ci0,j0c_{i_0,j_0} denote the corresponding coefficient of ff. Converse Hasse–Witt rank conjecture. The rank of the Hasse–Witt matrix of CfC'_f is at least gρg-\rho, and this bound is attained if and only if ci0,j0=0c_{i_0,j_0}=0 for every such solution (i0,j0)(i_0,j_0). This conjectured converse would give a geometric interpretation of the stated condition on the coefficients, complementing the proved implication from the coefficient condition to the Hasse–Witt rank bound.

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Primary source

Wouter Castryck, Marco Streng and Damiano Testa, “Curves in characteristic 2 with non-trivial 2-torsion”, arXiv:1402.3241 (2020).

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