These could be written as swappings: (AE) (BD) (CG) (FH) in the first case and (AE) (BF) (CG) (DH) in the second.
这些可以写成对换的形式：在第一个例子中是（AE）（BD）（CG）（FH），第二个例子中是（AE）（BF）（CG）（DH）。
There was a practical advantage to this Enigma property.
谜机的这种性质，在实践中有一种优势，
It meant that the deciphering operation was identical with the enciphering operation.
谜机的这种性质，在实践中有一种优势，
(In group-theory terms, the cipher was self-inverse).
用群论的术语来说，密码是自反的。
The receiver of the message had only to set up the machine in exactly the same way as the sender, and feed in the cipher-text, to recover the plain-text.
接收方只要把机器设置成与发送方相同的模式，然后将收到的密文输入进去，就能解码得到明文。
There was no need to incorporate 'encipher' and 'decipher' modes into the Enigma machine, which made its operation that much less liable to mistakes and confusion.
这样，谜机就不需要区分编码和解码两种不同模式，这使它变得更加可靠，不容易产生错误和混乱。
But it was associated with a grave weakness, in that the substitutions thus performed were always of this very special kind, with the particular feature that no letter could ever be enciphered into itself.
但是这也产生了一个严重的缺陷：谜机的替换规则总是这样一种特殊的形式，因此每个字母在编码之后都不可能是其本身。
This was the basic structure of the Enigma.
这是基础版谜机的构造，
But there was much more to the machine actually in military use.
但其军用版并不只是这样。
For one thing, the three rotors were not fixed in place, but could be removed and replaced in any order.
一方面，那三个转盘不是固定的，它们可以任意移动或更换。
Until late 1938 there was a stock of just three rotors, which therefore allowed a total of six arrangements.
在1938年后期，只制造了三种转盘，但它们可以按照6种不同的顺序安装。
In this way, the machine offered 6 × 17576 = 105456 different alphabetic substitutions.
因此，这个机器就能产生6×17576=105, 456种不同的替换规则。