 Complete the following phrase:  On 20 September 1940 at about 2 pm Genevieve Grotjan, carrying a set of work sheets walked up to a group of men engrossed in conversation and politely attempted to get Frank Rowletts attention. She had found evidence of cycles in the twenties cipher. Celebration ensued at this first break in the 20s cipher and it soon enabled a replica machine to be built. A pair of other messages using indicator 59173 were decrypted by 27 September, coincidentally the date that the 