This is a chess proverb for beginners of Go. In the corner, you can use the least pieces to enclose the largest space, followed by the side, while the middle belly looks rough, but it is the most difficult for beginners to become empty. This can also be seen from the structure of the chessboard. There are two side lines on the corner, so long as the other two sides are sealed, they can be empty, three sides should be sealed, and four sides should be sealed in the middle, so it is said to be "Jinjiao silver-edged grass belly"