1, set and elements of set are two different concepts, which are given by description in textbooks, similar to the concepts of points and lines in plane geometry.

2. The elements in the set are deterministic, different and out of order.

3.Set has two meanings: all eligible objects are its elements; As long as it is an element, you must sign the condition.

4. Set is a basic concept in mathematics. Basic concepts are concepts that cannot be defined by other concepts. The concept of set can be defined in an intuitive and axiomatic way.

5. Collection is to put people's intuition or thinking about certain identifiable objects together to make them a whole (or monomer), and this whole is a collection. Those objects that make up a set are called elements of this set (or simply elements).

nature

For any set a, an empty set is a subset of a:? Answer: Answer.

For any set a, the union of empty set and a is a:? A: A ∨? = A .

For any nonempty set A, the proper subset whose empty set is A:? A, if A≦? And then what? Really contained in a.

For any set a, the intersection of an empty set and a is an empty set:? One, one? = ? .

For any set a, an empty set and the cartesian product of a are all empty sets:? One, one ×? = ? .

The only subset of an empty set is the empty set itself:? A, if a? A, so A= ; ? A, if A=? So a? Answer.