Exercise 23 Page 197

A subset of a set is also a set. The requirement is that all elements in the subset are also elements of the set. We can list all the subsets starting with the ones having 0 elements, followed by 1 element.

Zero-Element Subsets

The only subset of any set with zero elements is the empty set. We write this using the empty set notation. ∅

One-Element Subsets

The original set has one element, so we can only form one subset having one element: the original set itself. { 1}

Summary

We have a total of 2 subsets. ∅, { 1}