+void
+Chord_tremolo_iterator::do_quit ()
+{
+ if (child_iter_)
+ child_iter_->quit ();
+}
+
+void
+Chord_tremolo_iterator::derived_mark () const
+{
+ if (child_iter_)
+ scm_gc_mark (child_iter_->self_scm ());
+}
+
+void
+Chord_tremolo_iterator::derived_substitute (Context *f, Context *t)