+We process commit sets from the bottom up according to the relation
+$\hasdep$. For each commit set $\pc$ we construct $\greffc$ from
+$\grefzc$, as planned. By construction, $\hasdep$ has $\patchof{L}$
+as its maximum, so this operation will finish by updating
+$\greffa{\patchof{L}}$.
+
+After we are done, the result has the following properties:
+\[ \eqn{Best Tip}{
+ \bigforall_{E_i \in \set E_{\pc}} \greffc \ge E_i
+}\]
+\[ \eqn{Perfect Contents}{
+ \greffc \haspatch \p \equiv \pc \hasdep \py
+}\]
+
+For brevity we will write $\grefu$ for $\grefuc$, etc. We will start
+out with $\grefc = \grefz$, and at each step of the way construct some
+$\grefu$ from $\grefc$. The final $\grefu$ becomes $\greff$.
+
+\subsection{Preparation}
+
+Firstly, we will check each $E_i$ for being $\ge \grefc$. If
+it is, are we fast forward to $E_i$
+--- formally, $\grefu = \text{max}(\grefc, E_i)$ ---
+and drop $E_i$ from the planned ordering.
+
+\subsection{Merge Contributors for UP TO HERE}