In mathematical symbols, it means within a range. Used to limit a number or variable to be valid within a certain range. For example, when we write down y ∈ [0, 1], it means that the number y must be between 0 and 1, otherwise the equation cannot be established. Therefore, mathematical symbols are often used in mathematics, which can help us describe problems and express mathematical relations more accurately.

Besides limiting the range of numbers, in mathematics, symbols can also be used to describe the elements in a set. When we write down x ∈ A, it means that X is an element in set A, and if we write down X? A means that X is not an element in set A. With this expression, we can easily describe the element relationship of various sets.

Mathematical symbols are also widely used in computer programming. Especially in Python, the in operator can be used to check whether an element is in a sequence. For example, if we want to check whether a number appears in a list, we can use the statement x in myList. This application makes mathematical symbols play an important role in modern science and technology.