def doi_exists(self, doi):
        """
        This method retrieve a boolean according to the existence of a crossref
        DOI number. It returns False if the API results a 404 status code.

        args: Crossref DOI id (String)

        return: Boolean

        Example 1:
            >>> from crossref.restful import Works
            >>> works = Works()
            >>> works.doi_exists('10.1590/S0004-28032013005000001')
            True

        Example 2:
            >>> from crossref.restful import Works
            >>> works = Works()
            >>> works.doi_exists('10.1590/S0004-28032013005000001_invalid_doi')
            False
        """
        request_url = build_url_endpoint(
            '/'.join([self.ENDPOINT, doi])
        )
        request_params = {}

        result = self.do_http_request(
            'get',
            request_url,
            data=request_params,
            only_headers=True,
            custom_header=str(self.etiquette)
        )

        if result.status_code == 404:
            return False

        return True