1. Euclid, Elements, proposition 7.32 (p. 219) and 9.20 (p. 271) from the Greek text of J. L. Heiberg (1883-1885), based on Euclidis Elementa, edited and translated in English by Richard Fitzpatrick [Online]. Available: https://farside.ph.utexas.edu/Books/Euclid/Elements.pdf
2. S. Hawking, God Created the Integers: The mathematical breakthroughs that changed history; Propositions 7.32 (p. 92) and 9.20 (p. 101); Running Press: Philadelphia, PA, USA, 2005.
3. G. H. Hardy and E. M. Wright, An Introduction to the Theory of Numbers, New York NY, USA: Oxford University Press, 2008 (6th edition), p. 23.
4. C. K. Caldwell, The Prime Pages: Goldbach's conjecture. [Online]. Available: https://t5k.org/glossary/page.php?sort=GoldbachConjecture
5. C. K. Caldwell, The Prime Pages: Prime Conjectures and Open Questions. [Online]. Available: https://t5k.org/notes/conjectures/