Last surviving characteristic of a settling fan
= Last surviving characteristic of a settling fan
{title2=$\phi_*=\sqrt A/(\sqrt A+\sqrt D)$}
If both <shocks> meet inside a <settling rarefaction fan>, $t_c=(\sqrt A+\sqrt D)^2/u_s$ and the last characteristic has concentration $\phi_*=\sqrt A/(\sqrt A+\sqrt D)$. It runs from the initial internal interface to the final deposit point. This construction requires $b\leq\phi_*\leq a$; otherwise a front exits the fan before final deposition.