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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 check_entitlement(doi):
 """Check whether IP and credentials enable access to content for a doi. This function uses the entitlement endpoint of the Elsevier API to check whether an article is available to a given institution. Note that this feature of the API is itself not available for all institution keys. """

    if doi.lower().startswith('doi:'):
        doi = doi[4:]
    url = '%s/%s' % (elsevier_entitlement_url, doi)
    params = {'httpAccept': 'text/xml'}
    res = requests.get(url, params, headers=ELSEVIER_KEYS)
    if not res.status_code == 200:
        logger.error('Could not check entitlements for article %s: '
                     'status code %d' % (doi, res.status_code))
        logger.error('Response content: %s' % res.text)
        return False
    return True