heads = scm_permanent_object (scm_cons (SCM_EOL, SCM_EOL));
scm_set_object_property_x (symbol, ly_symbol2scm ("stencil-head?"), SCM_BOOL_T);
heads = scm_permanent_object (scm_cons (SCM_EOL, SCM_EOL));
scm_set_object_property_x (symbol, ly_symbol2scm ("stencil-head?"), SCM_BOOL_T);