Cajori, Florian (1993). A History of Mathematical Notations. Mineola, New York: Dover Publications.
Boyer, Carl B. (1991), A History of Mathematics (Second ed.), John Wiley & Sons, Inc., ISBN 978-0-471-54397-8 978-0-471-54397-8
"Earliest Uses of Symbols for Matrices and Vectors". jeff560.tripod.com. Retrieved 18 December 2016. http://jeff560.tripod.com/matrices.html
"Earliest Uses of Symbols for Matrices and Vectors". jeff560.tripod.com. Retrieved 18 December 2016. http://jeff560.tripod.com/matrices.html
"Earliest Uses of Symbols for Matrices and Vectors". jeff560.tripod.com. Retrieved 18 December 2016. http://jeff560.tripod.com/matrices.html
Weil, André (1992), The Apprenticeship of a Mathematician, Springer, p. 114, ISBN 9783764326500. 9783764326500
Halmos, Paul (1950). Measure Theory. New York: Van Nostrand. pp. vi. The symbol ∎ is used throughout the entire book in place of such phrases as "Q.E.D." or "This completes the proof of the theorem" to signal the end of a proof.
Kenneth E. Iverson (1962), A Programming Language, Wiley, retrieved 20 April 2016 /wiki/Kenneth_E._Iverson