A.E. Crawley, “Magical Circle,” in Encyclopedia of Religion and Ethics, ed. James Hastings, vol. 8, pp. 321–324; J. Trachtenberg, Jewish Magic and Superstition: A Study in Folk Religion (repr. New York: Atheneum, 1974), p. 121; P. Schäfer, “Jewish Magic Literature in Late Antiquity and Early Middle Ages,” Journal of Jewish Studies 41 (1990), pp. 87–88.