(1942). Secret and urgent: The story of codes and ciphers / by Fletcher Pratt.
Chicago-čujuhus (17. p.)Secret and Urgent: The Story of Codes and Ciphers / by Fletcher Pratt. 1942.
MLA-čujuhus (9. p.)Secret and Urgent: The Story of Codes and Ciphers / by Fletcher Pratt. 1942.
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