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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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))