static <A extends Concept> A uniqueConcept(Class<A> c, O... params) {
  ret uniqueConcept(db_mainConcepts(), c, params);
}

static <A extends Concept> A uniqueConcept(Concepts cc, Class<A> c, O... params) {
  ret withDBLock(concepts, func -> A { 
    params = expandParams(c, params);
    A x = findConceptWhere(cc, c, params);
    if (x == null) {
      x = unlisted(c);
      csetAll(x, params);
      cc.register(x);
    }
    ret x;
  });
}