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

    MATERIAL_MAP = {
        'Article': 'publication',
        'Published thesis as a book': 'publication',
    }

    material = value.get('e') or value.get('3')

    return {
        'holder': value.get('d'),
        'material': MATERIAL_MAP.get(material),
        'statement': value.get('f'),
        'url': value.get('u'),
        'year': maybe_int(value.get('g')),
    }