Based on this break, with several more days’ work Randy solves Arethusa entirely. He comes up, in other words, with A(x) = K , such that for any given date x he can figure out what K , the keystream for that day would be; and just to prove it, he has the computer crank out K for every day in 1944 and 1945 and then use them to decrypt the Arethusa intercepts that came in on those days (without displaying them) and does the frequency count on them and verifies that it worked in each case.