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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 publication_info(self, key, value):
 """Populate the ``publication_info`` key."""

    def _get_cnum(value):
        w_value = force_single_element(value.get('w', ''))
        normalized_w_value = w_value.replace('/', '-').upper()

        return normalized_w_value

    def _get_material(value):
        schema = load_schema('elements/material')
        valid_materials = schema['enum']

        m_value = force_single_element(value.get('m', ''))
        normalized_m_value = m_value.lower()

        if normalized_m_value in valid_materials:
            return normalized_m_value

    def _get_parent_isbn(value):
        z_value = force_single_element(value.get('z', ''))
        if z_value:
            return normalize_isbn(z_value)

    def _get_pubinfo_freetext(value):
        x_value = force_single_element(value.get('x', ''))
        if not x_value.startswith('#DONE'):
            return x_value

    page_start, page_end, artid = split_page_artid(value.get('c'))

    parent_recid = maybe_int(force_single_element(value.get('0')))
    parent_record = get_record_ref(parent_recid, 'literature')

    journal_recid = maybe_int(force_single_element(value.get('1')))
    journal_record = get_record_ref(journal_recid, 'journals')

    conference_recid = maybe_int(force_single_element(value.get('2')))
    conference_record = get_record_ref(conference_recid, 'conferences')

    return {
        'artid': artid,
        'cnum': _get_cnum(value),
        'conf_acronym': force_single_element(value.get('q')),
        'conference_record': conference_record,
        'hidden': key.startswith('7731') or None,
        'journal_issue': force_single_element(value.get('n')),
        'journal_record': journal_record,
        'journal_title': force_single_element(value.get('p')),
        'journal_volume': force_single_element(value.get('v')),
        'material': _get_material(value),
        'page_end': page_end,
        'page_start': page_start,
        'parent_isbn': _get_parent_isbn(value),
        'parent_record': parent_record,
        'parent_report_number': force_single_element(value.get('r')),
        'pubinfo_freetext': _get_pubinfo_freetext(value),
        'year': maybe_int(force_single_element(value.get('y'))),
    }