DECLARE_SCHEME_CALLBACK (height, (SCM));
DECLARE_SCHEME_CALLBACK (outside_slur_callback, (SCM, SCM));
DECLARE_SCHEME_CALLBACK (pure_outside_slur_callback, (SCM, SCM, SCM, SCM));
DECLARE_SCHEME_CALLBACK (height, (SCM));
DECLARE_SCHEME_CALLBACK (outside_slur_callback, (SCM, SCM));
DECLARE_SCHEME_CALLBACK (pure_outside_slur_callback, (SCM, SCM, SCM, SCM));