The Stacks project

The concept of a Koszul-regular immersion was introduced in [Expose VII, Definition 1.4, SGA6] where it was called a regular immersion.

Definition 31.21.1. Let $i : Z \to X$ be an immersion of schemes. Choose an open subscheme $U \subset X$ such that $i$ identifies $Z$ with a closed subscheme of $U$ and denote $\mathcal{I} \subset \mathcal{O}_ U$ the corresponding quasi-coherent sheaf of ideals.

  1. We say $i$ is a regular immersion if $\mathcal{I}$ is regular.

  2. We say $i$ is a Koszul-regular immersion if $\mathcal{I}$ is Koszul-regular.

  3. We say $i$ is a $H_1$-regular immersion if $\mathcal{I}$ is $H_1$-regular.

  4. We say $i$ is a quasi-regular immersion if $\mathcal{I}$ is quasi-regular.

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View Definition 31.21.1 as pdf