static <A extends Concept> A uniqueConcept(Class<A> c, O... params) {
  params = expandParams(c, params);
  A x = findConceptWhere(c, params);
  if (x == null) {
    x = nuObject(c);
    for (int i = 0; i+1 < l(params); i += 2)
      cset(x, (S) params[i], params[i+1]);
  }
  ret x;
}