Execute $\alg{Fixup-Base}(W,\pc)$.
+TODO define Fixup-Base
+
\subsubsection{Result}
If all of that was successful, let $\tipcn = W$.
For each operation called for by the traversal algorithms, we prove
that the commit generation preconditions are met.
+WIP WHAT ABOUT PROVING ALL THE TRAVERSAL RESULTS
+
\subsection{Base Dependency Merge, Base Sibling Merge}
We do not prove that the preconditions are met. Instead, we check
them at runtime. If they turn out not to be met, we abandon
\alg{Merge-Base} and resort to \alg{Recreate-Base}.
+TODO COMPLETE MERGE-BASE STUFF
+
WIP WHAT ABOUT PROVING ALL THE TRAVERSAL RESULTS
\subsection{Tip Base Merge}