Computing the closure of a support

Abstract

When $E$ is an $R$-module over a commutative unital ring $R$, the Zariski closure of its support is of the form $\mathrm{V}(\mathcal{O}(E))$ where $\mathcal{O}(E)$ is a unique radical ideal. We give an explicit form of $\mathcal{O}(E)$ and study its behavior under various operations of algebra. Applications are given, in particular for ring extensions of commutative unital rings whose supports are closed. We provide some applications to crucial and critical ideals of ring extensions.