+ DECLARE_SCHEME_CALLBACK (pure_height, (SCM smob, SCM start, SCM end));
+ DECLARE_SCHEME_CALLBACK (calc_skylines, (SCM smob));
+ DECLARE_SCHEME_CALLBACK (combine_skylines, (SCM smob));
+ DECLARE_SCHEME_CALLBACK (calc_max_stretch, (SCM smob));
+ DECLARE_SCHEME_CALLBACK (print, (SCM smob));
+ DECLARE_SCHEME_CALLBACK (adjacent_pure_heights, (SCM));