DECLARE_SCHEME_CALLBACK (unfolded_music_length, (SCM));
DECLARE_SCHEME_CALLBACK (volta_music_length, (SCM));
DECLARE_SCHEME_CALLBACK (folded_music_length, (SCM));
DECLARE_SCHEME_CALLBACK (unfolded_music_length, (SCM));
DECLARE_SCHEME_CALLBACK (volta_music_length, (SCM));
DECLARE_SCHEME_CALLBACK (folded_music_length, (SCM));