static L<Int> virtualCountList(int n) {
  ret new RandomAccessAbstractList<Int>() {
    public int size() { ret n; }
    public Int get(int i) { ret i; }
  };
}

// to is exclusive
static L<Int> virtualCountList(int from, int to) {
  int n = max(to-from, 0);
  ret new RandomAccessAbstractList<Int>() {
    public int size() { ret n; }
    public Int get(int i) { ret from+i; }
  };
}