DECLARE_SCHEME_CALLBACK (calc_y_offset, (SCM));
DECLARE_SCHEME_CALLBACK (pure_calc_y_offset, (SCM, SCM, SCM));
DECLARE_SCHEME_CALLBACK (calc_x_offset, (SCM));
DECLARE_SCHEME_CALLBACK (calc_y_offset, (SCM));
DECLARE_SCHEME_CALLBACK (pure_calc_y_offset, (SCM, SCM, SCM));
DECLARE_SCHEME_CALLBACK (calc_x_offset, (SCM));