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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 retrieve_diaspora_host_meta(host):
 """ Retrieve a remote Diaspora host-meta document. :arg host: Host to retrieve from :returns: ``XRD`` instance """

    document, code, exception = fetch_document(host=host, path="/.well-known/host-meta")
    if exception:
        return None
    xrd = XRD.parse_xrd(document)
    return xrd