public boolean equal( State other ){
    if( other instanceof NaiveSudokuBoardState ){
      NaiveSudokuBoardState other_state = (NaiveSudokuBoardState)other;
      boolean flag = true;
      for( int i=0; i<n && flag;i++){
          for( int j=0;j<n && flag;j++){
            flag = (board.get(i,j) == other_state.board.get(i,j));
          }
      }
      return flag;
    }
    return false;
  }