Mathematical opening is union up and intersection down.

There are many operations between real numbers, such as addition, subtraction, multiplication, division, multiplication, square root and so on. If there are operations between sets, there are operations between sets, which are just called union, intersection and complement.

proper subset

Concept: If set B is a subset of set A and at least one element in set A does not belong to set B, then set B.

Proper subset called set A. B? A (or b? A "). , read "A really contains B" (or "B really contains A").

A subset that does not contain itself is called a proper subset. For sets a, b and c, if a? B，B？ C what about a? C.

Parallel search set in computer science

In computer science, the data structure of disjoint set is a kind of data structure, which is used to deal with the problems of merging and querying disjoint sets (a series of sets without repeated elements).

1. query: query which collection an element belongs to, and usually return a "representative element" in the collection. This operation is used to determine whether two elements are in the same collection.

2. Merge: merge two sets into one.

3. Add: Add a new collection with new elements. Add operations are not as important as query and merge operations and are often ignored.