The intersection of set A and set B is equal to set B, which means that all elements in set A are already contained in set B, that is, set A is a subset of set B ... set A is indeed contained in set B.

Set is a basic concept in mathematics.

If X is an element of set A, it is called X ∈ A. A set is a collection of certain and distinguishable objects in people's intuition or thinking to make it a whole (or called monomer). This whole thing is a set. Those objects that make up a set are called elements of this set (or simply elements).

There are two relationships between elements and sets: attribution and non-attribution.