sclass AOA_CompareImagesToProtos implements Steppable {
  new Map<S, BWImage> images;
  new Map<S, BWImage> protos;
  
  new AllOnAll<S> allOnAll;
  new Map<S, Scored<S>> bestProtoForImage;
  new Map<S, Scored<S>> bestImageForProto;
  
  public bool step() {
    PairS p = allOnAll.next();
    if (p == null) false;
    BWImage img1 = images.get(p.a);
    BWImage img2 = protos.get(p.a);
    Scored<S> bestProto = bestProtoForImage.get(p.a);
    float sim = bwImageSimilarityResized(img1, img2, score(bestProto));
    scoredMapPut(bestProtoForImage, p.a, p.b, sim);
    scoredMapPut(bestImageForProto, p.b, p.a, sim);
    true;
  }
  
  Map<S, Double> scoresForProtos() {
    ret mapKeyAndFunction(bestImageForProto, (proto, scored) -> score(scored));
  }
}