"Classification" is the abbreviation of transformation and attribution. Its basic idea is that when people solve problems, they often turn one problem they expect to solve into another one that can be solved well through some transformation means. In this way, the first problem can be solved by this easy problem.

Specific principles of classification: generally from abstract to concrete, when solving problems, turn them into more concrete and easy directions.

In this way, we can make full use of what we have learned and try to solve problems in simple and easy-to-understand ways.