Principal open subscheme (source code)

= Principal open subscheme
{title2=$D(f)$}
{wiki=Zariski_topology#Topology}

For $f\in A$, the principal open subset $D(f)=\{\mathfrak p:f\notin\mathfrak p\}$ of $\operatorname{Spec}A$ is the <affine scheme> $\operatorname{Spec}A_f$.