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

static <A extends Concept> Collection<S> distinctCIFieldValuesOfConcepts(Concepts concepts, Class<A> c, S field) {
  // indexed
  IFieldIndex<A, S> index = concepts.getCIFieldIndex(c, field);
  if (index != null)
    ret index.allValues();

  // table scan
  Set<S> set = ciSet();
  for (A x : concepts.list(c)) set.add((S) getOpt(x, field));
  ret set;
}