The topmost patch which we are trying to update. This and
all of its dependencies will be updated.
-\item[ $h : \pc^{+/-} \mapsto \set H_{\pc^{+/-}}$ ]
+\item[ $h : \pc^{+/-} \mapsto \set H^{\pc^{+/-}}$ ]
Function for getting the existing heads $\set H$ of the branch $\pc^{+/-}$.
These are the heads which will be merged and used in this update.
This will include the current local and remote git refs, as desired.