^Elkins, T H (1972). Germany (3rd ed.). London: Chatto & Windus, p. 13. ASINB0011Z9KJA.
^N.B. In German die Mittelgebirge (plural) refers to the Central Uplands; das Mittelgebirge refers to a low mountain range or upland region (Mittel = "medium" and -gebirge = "range").