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