static F1<RGBImage, Rect> trainFaceFinderX1() {
  new Best<F1<RGBImage, Rect>> best;
  for (int width = 8; width <= 32; width++) {
    L<RGBImageAndRect> images = markedFaces_scaledToWidth(width);
    int h = first(images).image.w();
    for (int y1 = 0; y1 < h; y1++)
     for (int y2 = y1+1; y2 <= h; y2++)
      for (int deltaX1 = -3; deltaX1 <= 0; deltaX1++)
       for (int deltaX2 = deltaX1+1; deltaX2 <= 3; deltaX2++)
        video_scoreRect_x_step(best, images, nu(FaceFinderX1, +y1, +y2, +deltaX1, +deltaX2, +width));
  }
  ret best!;
}

Began life as a copy of #1019204