Subset is a mathematical concept: if any element of set A is an element of set B, then set A is called a subset of set B ... Symbolic language: If? A∈A, there are all a∈B, what about A? B.
If any element of set A is an element of set B (any a∈A is a∈B), then set A is called a subset of set B, and is denoted as A? B or? b？ A, read as "set A is contained in set B" or set B contains set A ".
Namely:? A∈A has a∈B, what about A? B.
For two sets A and B, if any element of set A is an element of set B, we say that set A is contained in set B, or set B contains set A, which means that set A is a subset of set B. ..
If any element of set A is an element of set B, and at least one element of set B does not belong to set A, then set A is called proper subset of set B, and an empty set is a subset of any set. Any set is a subset of itself. An empty set is the proper subset of any non-empty set.
Set is a basic concept in mathematics and the main research object of set theory. The basic theory of set theory was founded in19th century. The simplest statement about set is the definition in naive set theory (the most primitive set theory), that is, set is "a certain pile of things" and the "things" in set are called elements.