## The most commonly used basic formulas

Let's assume that there are no marked mines around the number to be determined (in the case of mines, please refer to the "subtraction principle" later).

(Unrelated numbers are hidden from the picture. The blue dots represent empty spaces and the red dots represent thunder.)

## One headed fixed form

"One end" refers to one side of a number (three vertical squares) being empty or bordered.

1、 Two at one end, two thunder;

(Right border of 2 in the figure)

(Inference) Equation 22: If 22 is at one end, then the third grid is not thunder. (Image is temporarily omitted)

2、 Formula 11: If 11 is on one end, then the three squares on the other side have no mines;

(11 in the figure, left border)

(The left side of 11 in the figure is clearly empty)

(Inference) Formula 111: If there are three 1 or 2 heads, then the middle one is thunder, and the other two are not thunder. (Image is temporarily omitted)

## Arbitrary position formula

3、 At any position, there is no thunder on the outer side of 1 and one thunder on the outer side of 2;

4、 3 in the middle, three mines;

5、 121 At any location, two 1 have lightning and 2 have no lightning;

6、 1221 at any position: Two 2 with lightning, 1 without lightning

The above formula has the same direction in both horizontal and vertical directions.

## Subtraction principle:

If mines are already marked around the number, subtract the number of mines around the number first, while keeping these mines blank in your mind, and then apply the formula.

Figure below: It is actually an 11 fixed formula, and the green dot can be opened

Below: There are two mines around 3 with a ratio of 3-2=1, and one mine around 2 with a ratio of 2-1=1. Therefore, it is simplified to 11 mode, and the two grids for drawing points can be directly opened.

Below: After subtraction, there are 12 fixed formulas, with red dots indicating thunder.

Below: According to the number 3 located at the top of the figure, if there is only one mine in the two unknown squares enclosed by the ellipse, then the number 3 below becomes 2, using the 12 formula. The blue dot is not mine, and the red dot is mine.