How to check if a function follows identity?

Question

For example, if we want to check if a function follow commutativity then we have to check $A * B = B * A $. So what is it for identity?

Comments

Good Explanations

Answer 1

Identity for Digital logic is $1$.

Hence if a operation ($*$) follow $ A * 1 = 1 * A = A $ then Operation is called to have identity.

Answer 2

A*I=I*A=A

Answer 3

An Identity is an element such that for any A :

A*I = A