1. In Memory of Jack Levine (1907–2005)
2. Bryden , J. 1993 .Best-kept Secret. Toronto : Lester , p. 165 – 166 , 172, 227 .
3. Budiansky , S. 2000 .Battle of Wits: The Complete Story of Codebreaking in World War II. New York : The Free Press , p. 245 – 247 .
4. Colossus