“…Recall that given \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$\mathscr{U}_r=\mathscr{U}(r,r(g-1))$\end{document}, the subvariety B 1 r , r ( g − 1) is a divisor which we will denote Θ r . Given a general \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$E\in \mathscr{U}_r$\end{document}, it is known that the map defined by ξ↦ξ⊗ E is an embedding (see 25). It is easy to check by degenerating E to a direct sum of r line bundles that if \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$\Theta _r|_{\rm {Pic}^0(C)}=\Theta _E$\end{document} is a divisor, then Θ E ∈ | r Θ|, where Θ is a translate of the Riemann theta divisor on \documentclass{article}\usepackage{amssymb,mathrsfs}\begin{document}\pagestyle{empty}$\rm {Pic}^0(C)$\end{document}.…”