static <A extends Concept> Cl<A> nuLike conceptsSortedByFields(Class<A> c, S... fields) {
  ret conceptsSortedByFields(db_mainConcepts(), c, fields);
}

static <A extends Concept> Cl<A> conceptsSortedByFields(Concepts concepts, Class<A> c, S... fields) {
  ret sortedByFields(concepts.list(c), fields);
}