+ return max (dist, 0.0);
+}
+
+bool
+Separation_item::is_empty (Grob *me)
+{
+ Skyline_pair *sky = Skyline_pair::unsmob (me->get_property ("horizontal-skylines"));
+ return (!sky || sky->is_empty ());
+}
+
+/*
+ Return the width of ME given that we are considering the object on
+ the LEFT.
+*/
+Skyline
+Separation_item::conditional_skyline (Grob *me, Grob *left)
+{
+ vector<Box> bs = boxes (me, left);
+ return Skyline (bs, 0.1, Y_AXIS, LEFT);
+}
+
+
+MAKE_SCHEME_CALLBACK (Separation_item, calc_skylines,1);
+SCM
+Separation_item::calc_skylines (SCM smob)
+{
+ Item *me = unsmob_item (smob);
+ vector<Box> bs = boxes (me, 0);
+ /* todo: the horizon_padding is somewhat arbitrary */
+ return Skyline_pair (bs, 0.1, Y_AXIS).smobbed_copy ();
+}
+
+/* if left is non-NULL, get the boxes corresponding to the
+ conditional-elements (conditioned on the grob LEFT). This
+ sounds more general than it is: conditional-elements are
+ always accidentals attached to a tied note.
+*/
+vector<Box>
+Separation_item::boxes (Grob *me, Grob *left)
+{
+ Item *item = dynamic_cast<Item *> (me);
+
+ int very_large = INT_MAX;
+ Paper_column *pc = item->get_column ();
+ vector<Box> out;
+ extract_grob_set (me, left ? "conditional-elements" : "elements", read_only_elts);
+ vector<Grob*> elts;