Pros and cons: A sheet of paper has two sides, AB, and A and B are each a separate version of the front and back;
Left and right rounds: A left B right side row of a version of the left and right rounds;
World round: A round on the bottom of a total of a version of the world wheel;
or:
1. The pros and cons are two versions, one is positive and the other is negative.
2, the left and right rounds are also called self-reflection (self-turnover), a version of the paper, turn left and right.
3, the world wheel, paper up and down for bite, a positive and negative line up and down, head to head or feet to feet.
It is customary to say that if it is the imposition, it is the difference between positive and negative printing, self-turnover, and rolling over.
Pictured:
Reprinted from: Hexun Blog