Uses horizontal skylines in accidental placement

lily/include/skyline.hh

Index: lily/include/skyline.hh
diff --git a/lily/include/skyline.hh b/lily/include/skyline.hh
index e6cd030627dd746dfcdfee8739590441d768bca9..b5ff628d30f2bf80c7e2ae770c83816e16e5fc24 100644
--- a/lily/include/skyline.hh
+++ b/lily/include/skyline.hh
@@ -90,6 +90,8 @@ public:
   Real height (Real airplane) const;
   Real max_height () const;
   Real max_height_position () const;
+  Real left () const;
+  Real right () const;
   void set_minimum_height (Real height);
   void clear ();
   bool is_empty () const;