Consider the set $\displaystyle X=\{a,b,c\}$

The collection of subsets are $\displaystyle \O,X,\{a,b\},\{b,c\},\{b\}$

The book says the one point set $\displaystyle \{b\}$ is not closed because its complement is not open. What is the complement of $\displaystyle \{b\}\mbox{?}$