update cs (RotateLetter l) =
  let Just i = S.findIndexL (== l) cs
      j = if i >= 4 then 1 else 0
  in update cs (Rotate (- (i + j + 1)))
update cs (RotateLetter l) =
  let Just i = S.findIndexL (== l) cs
      j = if i >= 4 then 1 else 0
  in update cs (Rotate (- (i + j + 1)))
update cs (RotateLetter l) =
  let Just i = S.findIndexL (== l) cs
      j = if i >= 4 then 1 else 0
  in update cs (Rotate (- (i + j + 1)))