def get_next_unassigned(board):
    """
    Get the next unassigned variable in the domain (no heuristic)
    @param board: list, Sudoku board. List of lists of variables, making up
                  a 2-D array of the board
    @return cell  Class instance of Variable; a cell of the Sudoku board
    """
    for row in board:
        for cell in row:
            if cell.get_domain_size() > 1:
                return cell

    raise ValueError('Everything seems to be assigned!')