sclass ChessOCR_BoardsFound {
  sclass ByFEN {
    double bestScore;
    Rect bestPosition;
    Set<Pair<Rect, Double>> boardPositions = synchroSet();
  }
  
  Map<S, ByFEN> byFEN = synchroMap();
  transient L onChange = synchroList(); // L<Runnable|voidfunc(S fen)>
  transient L onImprovedScore = synchroList(); // L<Runnable|voidfunc(S fen, Rect)>
  
  void add(ChessOCR_RecognizedBoard b) {
    if (b == null || b.fen == null) ret;
    ByFEN bf = getOrCreate ByFEN(byFEN, b.fen);
    bool change;
    if (b.rectInOriginalImage != null)
      if (bf.boardPositions.add(pair(b.rectInOriginalImage, b.score))) set change;
    if (b.score > bf.bestScore) {
      bf.bestScore = b.score;
      bf.bestPosition = b.rectInOriginalImage;
      pcallFAll(onImprovedScore, b.fen, bf.bestPosition);
      set change;
    }
    if (change) pcallFAll(onChange, b.fen);
  }
}