2015. Kaplan Publishing. p. 299. ISBN 978-1-61865-686-5 ^ a b Thomas Hungerford; Douglas Shaw (2008). Contemporary Precalculus: A Graphing Approach. Cengage
Stillwell (1980, 2ed 1993, ISBN 978-0-3879-7970-0) Algebra, Thomas W. Hungerford (1974, ISBN 978-0-387-90518-1) Multiplicative Number Theory, Harold Davenport
at the Wayback Machine. (April 30, 1996) ^ "1987: Gunman kills 14 in Hungerford rampage", On this day August 19. BBC, Retrieved August 6, 2008 ^ “'Ryan