In mathematics, an interval usually refers to a set of real numbers: if X and Y are two numbers in a set, then any number between X and Y also belongs to the set.

Concept:

Let a and b be two real numbers, a.

1, the set of real numbers x satisfying the inequality a≤x≤b is called a closed interval, which means [a, b].

2. satisfy inequality a

3. Satisfy the inequality A ≤ X.

4. The set of real numbers X satisfying the inequality x>A or x < A is called infinite interval, which means (a, +∞), (-∞, a).

5.(+∞, -∞)=R (real number set).

Interval definition:

Interval plays an important role in integral theory, because as the simplest set of real numbers, they can be easily defined as "length" or "measure". Then, we can extend the concept of "measure" and introduce Borel measure and Lebesgue measure.

Interval is also the core concept of interval arithmetic. Interval arithmetic is a numerical analysis method used to calculate rounding error.

The concept of interval can also be extended to any subset S of totally ordered set T, so that if both X and Y belong to S, and X