First of all, it is necessary to understand that the bottom of a closely packed hexagon is a hexagon (it seems to be a regular hexagon, right? ), so for the convenience of calculation, it sets the coordinates to three directions with the bottom as the included angle 120 degrees, and then forms a new coordinate space, in which one surface is perpendicular to the bottom, so the sliding surface and sliding surface are represented by four digits.

Slip surface: {000 1} refers to the surface formed by connecting points on each coordinate axis, which seems to refer to countless surfaces here;

Slip: It was originally an arrow composed of the origin and this point, and it seems to be a surface here;

Of course, this coordinate system can be converted with the rectangular space coordinate system, and the specific mathematical calculations can be piled up slowly. Alas, the foundation of materials science has been forgotten for three years.