// virtual view into a list that with a "gap" (elements in the middle being removed)
static <A> L<A> lineComp_listWithGap(L<A> l, int copyTo, int copyFrom) {
  if (copyFrom == copyTo) ret l;
  ret new RandomAccessAbstractList<A> {
    int size = l.size()-(copyFrom-copyTo);
    public int size() { ret size; }
    public A get(int i) {
      ret l.get(i < copyTo ? i : i+(copyFrom-copyTo));
    }
  };
}