The residue field as an infinite syzygy

Jian Liu; Justin Lyle

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arXiv · 2610.38393

The residue field as an infinite syzygy

Jian Liu·Justin Lyle

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Abstract

Let $(R,\mathfrak{m},k)$ be a commutative Noetherian ring which is either local or positively graded over the field $k$. We provide a method based on liftings for constructing free coresolutions of $k$ over $R$. We apply this method to twisted trivial extensions of the node $k[u,v]/(uv)$ to build a family of positively graded $k$-algebras of dimension $1$ over which $k$ is an infinite graded syzygy, resolving an open question of Iyengar in the negative. We also prove a formula for alternating sums of lengths of Ext modules when $R$ is positively graded, and use it to show that a graded free coresolution of $k$ cannot dualize to a resolution unless $R$ is Artinian Gorenstein.

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Jian Liu, Justin Lyle. 2026-10-28. The residue field as an infinite syzygy. https://arxiv.org/abs/2610.38393

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