## Thinking Mathematically (6th Edition)

false $\{\emptyset\} \subseteq \{\emptyset, \{\emptyset\}\}$
$\{\emptyset\} \not\subseteq \{\emptyset, \{\emptyset\}\}$ This is incorrect, for it should say: $\{\emptyset\} \subseteq \{\emptyset, \{\emptyset\}\}$ Let's say: $A=\{\emptyset\}$ $B=\{\emptyset, \{\emptyset\}\}$ We can see that A's only element is an empty set ($\emptyset$). An empty set ($\emptyset$) is also an element of B. Therefore: $A\subseteq B$