DECLARE_SCHEME_CALLBACK (minimum_start_callback, (SCM));
DECLARE_SCHEME_CALLBACK (first_start_callback, (SCM));
DECLARE_SCHEME_CALLBACK (simultaneous_relative_callback, (SCM, SCM));
DECLARE_SCHEME_CALLBACK (event_chord_relative_callback, (SCM, SCM));
DECLARE_SCHEME_CALLBACK (minimum_start_callback, (SCM));
DECLARE_SCHEME_CALLBACK (first_start_callback, (SCM));
DECLARE_SCHEME_CALLBACK (simultaneous_relative_callback, (SCM, SCM));
DECLARE_SCHEME_CALLBACK (event_chord_relative_callback, (SCM, SCM));