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) {
  params = expandParams(c, params);
  A x = findConceptWhere(cc, c, params);
  if (x == null) {
    x = unlisted(c);
    csetAll(x, params);
    cc.register(x);
  }
  ret x;
}