Z: integer set {…,-1, 0, 1, …}

Q: Rational number set

R: set of real numbers (including rational numbers and irrational numbers)

R+: positive real number set

R-: negative real number set

C: complex set

: empty set (a set without any elements)

N* or N+: positive integer set {1, 2,3, …}

Q+: Set of Positive Rational Numbers

Q-: set of negative rational numbers

Extended data:

Features of this kit:

1, certainty

Given a set, any element, whether it belongs to the set or not, must be one of them, and there is no ambiguity.

2. Interrelation

Any two elements in a collection are considered different, that is, each element can only appear once. Sometimes it is necessary to describe the situation where the same element appears many times. You can use multiset, where elements are allowed to appear multiple times.

3. Chaos

In a set, the state of each element is the same and the elements are out of order. You can define an order relation on the set. After defining the order relation, you can sort the elements according to the order relation. But as far as the characteristics of the set itself are concerned, there is no necessary order between elements.