static L<Rect> scaleRects(L<Rect> rects, double factor) {
  new L<Rect> l;
  for (Rect r : rects)
    l.add(scaleRect(r, factor));
  ret l;
}

static L<Rect> scaleRects(double factor, L<Rect> rects) {
  ret scaleRects(rects, factor);
}