# Is every affine open subset of a locally Noetherian scheme also Noetherian?

Ravi Vakil definition 5.3.4.

Suppose $X$ is a scheme. If $X$ can be covered by affine open sets Spec($A$) where $A$ is Noetherian, we say that $X$ is a locally Noetherian scheme.

The definition only says "If $X$ can be covered by affine open sets Spec($A$) where $A$ is Noetherian". I wonder if this can imply that every affine open set is Northerian?

Yes, because an affine scheme is quasicompact. So, if $U\subseteq X$ is an affine open subscheme, then $U$ is covered by finitely many spectra of Noetherian rings and so is Noetherian.