static <A extends Concept> ConceptFieldIndexCI_withTopTen<A> indexConceptFieldCIWithTopTen(Concepts cc default db_mainConcepts(), Class<A> c, S field) {
  var idx = getConceptFieldCIIndex(cc, c, field);
  if (idx cast ConceptFieldIndexCI_withTopTen)
    ret idx;
    
  // replace existing index without top ten
  if (idx != null)
    cc.removeCIFieldIndex(c, field);
    
  ret new ConceptFieldIndexCI_withTopTen(cc, c, field);
}