+vector<int>
+Note_collision_interface::note_head_positions (Grob *me)
+{
+ vector<int> out;
+ extract_grob_set (me, "elements", elts);
+ for (vsize i = 0; i < elts.size (); i++)
+ if (Grob *stem = unsmob_grob (elts[i]->get_object ("stem")))
+ {
+ vector<int> nhp = Stem::note_head_positions (stem);
+ out.insert (out.end (), nhp.begin (), nhp.end ());
+ }
+
+ vector_sort (out, less<int> ());
+ return out;
+}
+