Solitons: Differential equations, symmetries, and infinite-dimensional algebras
《Solitons: Differential equations, symmetries, and infinite-dimensional algebras》 · 第 181 页 · Section 7.5「Tensor products, duals and homomorphisms」
We say that an $\mathcal O_X$-module $\mathcal L$ is invertible if $\mathcal L$ is locally free of rank $1$. We see that the set of isomorphism classes of invertible $\mathcal O_X$-modules forms a group, the so-called Picard group $\operatorname{Pic}(X)$ of $X$.