Rejewski modeled the machine as permutation made from permutations of plugboard (), the wiring from the keyboard/lamps to the rotors (), the three rotors (), and the reflector (). The permutation for each position of the doubled key was different, but they were related by a permutation that represented a single step of a rotor ( is known). Rejewski assumed that the left and middle rotors did not move while encrypting the doubled key. The six letters of the doubled key consequently see the permutations A B C D E F: