The magic mirror is a kind of precious mirror mentioned many times in The Journey to the West's novels, which is used to shine on demons. No matter what the goblin becomes, as long as you look in the magic mirror, you will immediately reveal your true colors. Any demon who is captured and reveals his true colors, even if it is Niu Wangmo, is "unable to move and escape" and has lost the ability to change his actions. Interestingly, in mathematics, there is indeed a magic mirror, that is, 66666...67. This number is endless. You can add as many 6' s as you want, but the last digit must be 7.
Suppose there is a digital goblin hiding its prototype. It is a multi-digit, but we don't know who it is. For the sake of explanation, we might as well assume that it is a four-digit number. Now, when you multiply by 6667, you don't have to fully reveal its result-of course, if you know the product, don't you know what it is to divide by 6667? We don't need to know the product of this number multiplied by 6667, just know its four tails, and then we can tell you what this number is.
Isn't this amazing? Kind of like fortune telling. It's true. As long as we have these four tails, we can expose it in broad daylight.
Use only one number to explain, for example, the tail of the product is 5632. After knowing this number, you can know that the original number must be 6896 by multiplying it by 3 and intercepting the last 4 digits.