Miller 2013, p. 15: "'Abd al-Qadir was careful, however, not to appear to challenge 'Abd al-Rahman's own claims of suzerainty, and made it known that he was acting merely as the Moroccan sultan's khalifa, or deputy. Still in theory a vassal of the Moroccan sultan" Miller, Susan (2013). A History of Modern Morocco. Cambridge University Press. ISBN978-0-521-81070-8.