/** {@link Rel} with ANY, not variables. */
public static Rel unvar(Rel r) {
if (r.getTuple().stream().allMatch(Rules::check)) return r;
// Tuple::map??
List<Node> x = r.getTuple().stream().map(n -> fUnvar.apply(n)).collect(Collectors.toList());
return new Rel(r.getName(), TupleFactory.create(x));
}
