Furthermore, Enigma permutations were simple transpositions, which meant that each permutation "A B C D E F" only transposed pairs of characters. Those character pairs had to come from different cycles of the same length. Moreover, any one pairing between two cycles determined all the other pairs in those cycles. Consequently, permutations "A" and "D" both had to transpose a and s because (a) and (s) are the only cycles of length one and there is only one way to pair them. There are two ways to match (bc) and (rw) because b must pair with either r or w. Similarly, there are ten ways to match the remaining ten-character cycles. In other words, Rejewski now knew that there were only twenty possibilities for the permutations "A" and "D". Similarly, there were 27 candidates for "B" and "E", and 13 candidates for "C" and "F".