1. G. Boole, An Investigation of The Laws of Thought, Walton and Maberly, London, 1854; reprinted Dover, New York, 1958.
2. A.W.F. Edwards, Cogwheels of the Mind: The Story of Venn Diagrams, Johns Hopkins University Press, Baltimore, 2004.
3. A.W.F. Edwards, “Euler diagrams and Venn diagrams” (letter), The Mathematical Intelligencer (2006), 28(3).
4. L. Euler, Lettres à une Princesse d’Allemagne, Imperial Academy of Sciences, St. Petersburg, 1768.
5. L. Euler, Letters to a German Princess, transl. H. Hunter, Murray, London, 1795.