For two sets A and B, if any element of set A is an element of set B, then set A is called a subset of set B. ..

Write: a? B or B? A

Meaning: proper subset (The old textbook says so, what about the new one? There is an inequality symbol below)

If set A is a subset of set B, but at least one element in b does not belong to A, then set A is the proper subset of set B, which can be written as

Answer? B or B? A