P in cursive script stands for force set. Let A be a set, and Hua P(A) also wrote in some books:

A

2 (written as "2 to the power of a")

Represents a power set, that is, each element in A has two situations: whether it is needed or not, so that all the combined sets are power sets. Include an empty set. For example, it is easy to understand.

Let A={ 1, 2,3}

So P(A)={? ,{ 1},{2},{3},{ 1,2},{ 1,3},{2,3},{ 1,2,3}}