commit we generate will have only reachable commits as ancestors, so
generating a new commit (only) adds that new commit to $\allreach$.
-\item[ $\allreachof{\py}$ ]
-The set of reachable commits at the point where we have just generated
-$\tippy$, i.e. just after $\alg{Merge-Tip}(\p)$.
+\item[ $\allreachof{\pn}$, $\allreachof{\py}$ ]
+The sets of reachable commits at the point where we have just generated
+$\tippn$ or $\tippy$, i.e. just after $\alg{Merge-Base}(\p)$ or
+$\alg{Recreate-Base}(\p)$, or $\alg{Merge-Tip}(\p)$, respectively.
\end{basedescript}