Set space, S={} This set can be all possible solutions, and the initial range can be the range after the derivation of the topic.

Then, according to the requirements of mathematical properties or topics, we divide S-set into a series of subsets of S=R 1UR2UR3 ... in order to continue to solve the problem. Elements in each subset can use the same kind of attributes when solving problems.

Generally speaking, when there are uncertain conditions, classification begins.

I don't know if I understand this.