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3. Friedman, Elizebeth S. “Voynich Manuscript.” Washington Post, August 5, 1962.
4. Friedman, William F. Elements of Cryptanalysis. Training Pamphlet No. 3. Washington, DC: Office of the Chief Signal Officer, 1923.
5. ———. “Letter to John M. Manly,” Friedman Collection. George Marshall Foundation Research Library, February 4, 1922.