sS chess_makeFEN(LL<S> recognized) {
  if (empty(recognized)) null;
  new LS out;
  for (LS row : recognized) {
    int i = 0;
    new StringBuilder buf;
    while (i < 8) {
      int j = smartIndexOfNot(row, "empty", i);
      if (j > i) {
        buf.append(j-i);
        i = j;
      } else {
        S p = row.get(i++);
        S piece = secondWord(p);
        char c = eq(piece, "knight") ? 'n' : first(piece);
        if (startsWith(p, "white")) c = upper(c);
        buf.append(c);
      }
    }
    out.add(str(buf));
  }
  ret join("/", out);
}