56. On the intertextuality of all discourses—with pointers for the analysis of cartography—see Tzvetan Todorov, Mikhail Bakhtin: The Dialogical Principle, trans. Wlad Godzich. Minneapolis: University of Minnesota Press, 1984: 60-74; also M. M. Bakhtin, The Dialogic Imagination: Four Essays, ed. Michael Holquist, trans. Caryl Emerson and Michael Holquist. Austin: University of Texas Press, 1981. I owe these references to Dr. Cordell Yee, History of Cartography Project, University of Wisconsin at Madison.