Vortex composition by conformal rescaling
= Vortex composition by conformal rescaling
If $u$ solves the Taubes equation for a metric $g$ and $\widetilde u$ solves it for $e^ug$, then $u+\widetilde u$ solves it for $g$. The vortex divisors add, so the total vortex number is $N+\widetilde N$.