Diophantine Geometry: An Introduction
《Diophantine Geometry: An Introduction》 · 第 108 页 · Exercises，A.5.6「Poincaré divisor」，构造段
The pair $(H,\chi)$ defines a divisor class $\mathcal P\in\operatorname{Pic}(A\times\widehat A)$. The divisor class $\mathcal P$ is called the Poincaré divisor class.