By the results of Tip Base Merge, $\baseof{W} = \tipcn$.
- By Base Ends Supreme, $\tipcn \ge \baseof{S}$ i.e.
+ By Base Ends Supreme TODO CHECK THIS, $\tipcn \ge \baseof{S}$ i.e.
$\baseof{R} \ge \baseof{L}$.
Either $\baseof{L} = \baseof{M}$, or we must choose a different $M$ in