+ Simultaneous_music_iterator (Simultaneous_music_iterator const &);
+ virtual void derived_substitute (Context *f, Context *t);
+ virtual void derived_mark () const;
+ DECLARE_SCHEME_CALLBACK (constructor, ());
+ DECLARE_CLASSNAME(Simultaneous_music_iterator);
+
+ /// make a new context for every child.
+ bool create_separate_contexts_;