Joseph Gregor Lang: Reise auf dem Rhein. Vol. 2. 1789, pp. 70, 85. Quoted from: Christoph Nebgen: Konfessionelle Differenzerfahrungen. Oldenbourg, Munich 2014, ISBN978-3-110-39576-1, p. 220 (Cologne–Düsseldorf rivalry, p. 220, at Google Books).
Philipp Wilhelm Gercken: Travels through Swabia, Bavaria, bordering Switzerland, Franconia, and the Rhenish Provinces etc. Stendal 1788. vol. 3, p. 255. Cited in: Christoph Nebgen: Konfessionelle Differenzerfahrungen. Oldenbourg, Munich 2014, ISBN978-3-110-39576-1, p. 218 (Cologne–Düsseldorf rivalry, p. 218, at Google Books).
Schleucher, René (17 November 2009). "Koelner-S-Bahn-nervt-Duesseldorf". Solinger Tageblatt. Archived from the original on 27 December 2014. Retrieved 15 December 2015.
Schleucher, René (17 November 2009). "Koelner-S-Bahn-nervt-Duesseldorf". Solinger Tageblatt. Archived from the original on 27 December 2014. Retrieved 15 December 2015.