Divisor class group of a plane-curve complement
= Divisor class group of a plane-curve complement
{title2=$\operatorname{Cl}(\mathbb P^2\setminus C)\simeq\mathbb Z/d\mathbb Z$}
If $C$ is an irreducible plane curve of degree $d$, the <localization sequence for the divisor class group> quotients $\operatorname{Cl}(\mathbb P^2)=\mathbb Z[H]$ by the class $[C]=d[H]$. Nonsingularity of the removed curve is not required; irreducibility makes it a single removed <prime Weil divisor>.