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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 adapt_package(package):
 """Adapts ``.epub.Package`` to a ``BinderItem`` and cascades the adaptation downward to ``DocumentItem`` and ``ResourceItem``. The results of this process provide the same interface as ``.models.Binder``, ``.models.Document`` and ``.models.Resource``. """

    navigation_item = package.navigation
    html = etree.parse(navigation_item.data)
    tree = parse_navigation_html_to_tree(html, navigation_item.name)
    return _node_to_model(tree, package)