Read tokens from the provided parse tree in the SNLI dataset.
    Illegal examples are removed.

def main(args):
    """
    Read tokens from the provided parse tree in the SNLI dataset.
    Illegal examples are removed.
    """
    examples = []
    with open(args.input, 'r') as fin:
        reader = csv.DictReader(fin, delimiter='\t')
        for cols in reader:
            s1 = read_tokens(cols['sentence1_parse'])
            s2 = read_tokens(cols['sentence2_parse'])
            label = cols['gold_label']
            if label in ('neutral', 'contradiction', 'entailment'):
                examples.append((s1, s2, label))
    with open(args.output, 'w') as fout:
        for s1, s2, l in examples:
            fout.write('{}\t{}\t{}\n'.format(' '.join(s1), ' '.join(s2), l))