How to divide the couplet into upper and lower lines?

One is to be divided according to the tone of the tone, the last word of the upper line is oblique, three and four for oblique, the last word of the lower line is flat, one and two for flat.

Secondly, according to the cause and effect relationship, "cause" for the first line, "fruit" for the second line, because there is a cause and then there is a result.

Thirdly, according to the time sequence, time in the first for the first line, time in the second for the second line.

Fourth, according to the spatial scope of points, generally the smaller in the front, the larger in the back.