static <A extends Concept> A nuLike highestConceptByField(Class<A> c, S field) {
  ret highestConceptByField(db_mainConcepts(), c, field);
}

static <A extends Concept> A highestConceptByField(Concepts concepts, Class<A> c, S field) {
  // indexed
  IFieldIndex<A, O> index = concepts.getFieldIndex(c, field);
  if (index cast ConceptFieldIndexDesc) {
    Map.Entry e = ((NavigableMap) index.valueToObject.data).firstEntry();
    ret e == null ? null : (A) first((Cl) e.getValue());
  }
  ret highestByField(field, concepts.list(c));
}