In mathematics, we often use the interior of a closed curve on a plane to represent a set. This kind of diagram is called a Venn diagram . In the future, it will be frequently used in the analysis of event relationships. It can clearly express the relationship between events geometrically and intuitively.

　　It is easy to see from the figure that the operation of events satisfies the following basic relationships :
　　(1) , , ;
　　(2) If , then , ;
　　(3) ,

　　　.

　　Note: Venn Diagram , sometimes called Venn diagram or Venn diagram, was first introduced by German physicist Wilhelm Carl Werner Otto Fritz Franz Wien (1864-1928) to representsets and their Relationship graphics. In 1911, he won the Nobel Prize in Physics for his contributions to physical laws such as thermal radiation.

　　For example, the relationship between commonly used specific number sets , , , , and can be represented by a Venn diagram as follows: