## Thinking Mathematically (6th Edition)

$A\in B$ $C\subseteq D$ The symbol $\in$ indicates that $A$ is a single element of the set $B$. The symbol $\subseteq$ indicates that all the elements of the set $C$ are also elements of the set $D$.
When we have: $A\in B$ $C\subseteq D$ The symbol $\in$ indicates that $A$ is a single element of the set $B$. The symbol $\subseteq$ indicates that all the elements of the set $C$ are also elements of the set $D$. Therefore, $A\in B$ and $A\subseteq B$ are not interchangeable.