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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 filter_publisher_references(root, head, update):
 """Remove references from ``update`` if there are any in ``head``. This is useful when merging a record from a publisher with an update form arXiv, as arXiv should never overwrite references from the publisher. """

    if 'references' in head:
        root = _remove_if_present(root, 'references')
        update = _remove_if_present(update, 'references')

    return root, head, update