+{- Note [Rewriting labelled LGraphs]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It's hugely annoying that we get in an LGraph and in order to solve it
+we have to slap on a new label which we then immediately strip off.
+But the alternative is to have all the iterative solvers work on
+Graphs, and then suddenly instead of a single case (ZBlock) every
+solver has to deal with two cases (ZBlock and ZTail). So until
+somebody comes along who is smart enough to do this and still leave
+the code understandable for mortals, it stays as it is.
+
+(One part of the solution will be postorder_dfs_from_except.)
+-}
+
+solve_and_rewrite_b_graph comp fuel graph exit_fact =
+ do g <- lgraphOfGraph graph
+ (fuel, a, g') <- solve_and_rewrite_b comp fuel g exit_fact
+ return (fuel, a, remove_entry_label g')
+