Make._val f_val : R.t list -> boolPredicate to check the validity of a priority class.
val f_r_val : R.t list -> boolPredicate to check the validity of a reducible priority class.
val f_val_err : R.t list -> stringA precise reason why f_val failed. Called only when f_val is false.
val f_r_val_err : R.t list -> stringA precise reason why f_r_val failed. Called only when f_r_val is false.