static <A> LinkedList<A> cloneLinkedList(Iterable<A> l) {
  ret l instanceof Collection ? cloneLinkedList((Collection) l) : asLinkedList(l);
}

static <A> LinkedList<A> cloneLinkedList(Collection<A> l) {
  if (l == null) ret new LinkedList;
  synchronized(collectionMutex(l)) {
    ret new LinkedList<A>(l);
  }
}