SCM ly_prob_set_property_x (SCM system, SCM sym, SCM value);
SCM ly_prob_property (SCM prob, SCM sym, SCM val);
SCM ly_prob_type_p (SCM obj, SCM sym);
SCM ly_prob_set_property_x (SCM system, SCM sym, SCM value);
SCM ly_prob_property (SCM prob, SCM sym, SCM val);
SCM ly_prob_type_p (SCM obj, SCM sym);