There are also lg(x? The domain of-1) is X > 1 and (and) x.

Comma: For example, {0, 1, 2, 3, 4, 5, 6} commas are used for separation. If there are n elements, there are n- 1 commas.

concept

A collection refers to a collection of concrete or abstract objects with certain attributes. Among them, these objects that make up the set are called elements of the set.

For example, the collection of all China people, its element is every China person. Generally, uppercase letters such as A, B, S, T, ... are used to represent a set, while lowercase letters such as A, B, X, Y, ... are used to represent elements in the set. If X is an element of the set S, it is said that X belongs to S and is marked as X ∈ S ... If Y is not an element of the set S, it is said that Y does not belong to S and is marked as Y? s .