From skew Combinatorial Nullstellensatz to sharp Ax-Katz congruences and zero counts
Abstract
We give a unified account of zero counting in finite-field polynomial rings with commuting variables twisted by a common automorphism. A decomposition into fixed-field slices connects skew evaluation with ordinary polynomial evaluation. First, we derive a slice coefficient formula from the skew Combinatorial Nullstellensatz and use it to deduce skew Chevalley-Warning, including the sufficient condition n>h∑i di. Next, classical Ax-Katz gives the corrected integer congruence Qmax{0,⌈(n−h∑i di)/D⌉}| N+(M−1)δ. We construct homogeneous examples proving optimality for every positive degree table and every number of variables. We also establish a sharp lower bound with a prescribed zero, an input-sensitive coefficient-filtration refinement, and transfers of known bounds for nonlinear zero sets. Detailed calculations explain the origin correction, incomplete norm blocks, and the distinction between characteristic-p summation and higher integer divisibility. Existing geometric, interpolation, and counting theorems are explicitly attributed.
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BibTeX
@misc{li2026from,
title = {{From skew Combinatorial Nullstellensatz to sharp Ax-Katz congruences and zero counts}},
author = {Shuang Li and Xuan Pang and Pingzhi Yuan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.35739},
eprint = {2610.35739},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.35739},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - From skew Combinatorial Nullstellensatz to sharp Ax-Katz congruences and zero counts
AU - Shuang Li
AU - Xuan Pang
AU - Pingzhi Yuan
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2610.35739
UR - https://arxiv.org/abs/2610.35739
AB - We give a unified account of zero counting in finite-field polynomial rings with commuting variables twisted by a common automorphism. A decomposition into fixed-field slices connects skew evaluation with ordinary polynomial evaluation. First, we derive a slice coefficient formula from the skew Combinatorial Nullstellensatz and use it to deduce skew Chevalley-Warning, including the sufficient condition n>h∑_i d_i. Next, classical Ax-Katz gives the corrected integer congruence Q^max{0,⌈(n−h∑_i d_i)/D⌉}| N+(M−1)δ. We construct homogeneous examples proving optimality for every positive degree table and every number of variables. We also establish a sharp lower bound with a prescribed zero, an input-sensitive coefficient-filtration refinement, and transfers of known bounds for nonlinear zero sets. Detailed calculations explain the origin correction, incomplete norm blocks, and the distinction between characteristic-p summation and higher integer divisibility. Existing geometric, interpolation, and counting theorems are explicitly attributed.
ER -