+ return sign (Staff_symbol_referencer::position_f ((Grob*)a) -
+ Staff_symbol_referencer::position_f ((Grob*)b));
+}
+
+
+void
+Staff_symbol_referencer::set_interface (Grob * e)
+{
+ if (!gh_number_p (e->get_grob_property ("staff-position")))
+ e->set_grob_property ("staff-position", gh_double2scm (0.0));