# Math Insight

### Proper subset definition

A proper subset of a set A is a subset of A that is not equal to A. In other words, if B is a proper subset of A, then all elements of B are in A but A contains at least one element that is not in B.

For example, if A =\{1,3,5\} then B=\{1,5\} is a proper subset of A. The set C=\{1,3,5\} is a subset of A, but it is not a proper subset of A since C=A. The set D=\{1,4\} is not even a subset of A, since 4 is not an element of A.