"the enigma never encrypts a letter to itself": I recall that the clue to one day's cypher was a longish document that contained every letter except 'L'. The

"the enigma never encrypts a letter to itself": I recall that the clue to one day's cypher was a longish document that contained every letter except 'L'. The analyst guessed that it was produced by somebody running a test who kept typing the letter 'L'--she was right.