The message key is three characters long, so the doubled key is six characters long. Rejewski labeled the permutations for the successive message-key characters "A B C D E F". He did not know what those permutations were, but he did know that "A" and "D" permutations encrypted the same message key letter, that "B" and "E" encrypted the same letter, and that "C" and "F" encrypted the same letter. If are the (unknown) plaintext letters of the message key and are the corresponding (known) ciphertext letters, then