def correction_score(typos, corrections):
    """
    Equal to score_at_k(typos, corrections, 1).
    """
    assert typos.shape[0] == corrections.shape[0]
    scores = {'tp': 0, 'fp': 0, 'tn': 0, 'fn': 0}
    for id in typos.index:
        if typos.loc[id, 'corrupted']:
            if corrections[id] == typos.loc[id, 'identifier']:
                scores['tp'] += 1
            else:
                scores['fn'] += 1
        elif corrections[id] == typos.loc[id, 'identifier']:
            scores['tn'] += 1
        else:
            scores['fp'] += 1
    return scores
