The expression $\emptyset \subseteq \emptyset$ (read as "the empty set is a subset of the empty set") is true.

Here's why:

• The empty set $\emptyset$ is a set that contains no elements.
• A set $A$ is considered a subset of another set $B$ (written $A \subseteq B$) if every element of $A$ is also an element of $B$.
• Since $\emptyset$ has no elements, the condition "every element of $\emptyset$ is also an element of $\emptyset$" is vacuously true. Therefore, $\emptyset$ is a subset of itself.

Thus, $\emptyset \subseteq \emptyset$ is indeed true.

Would you like more details or have any questions?

Here are five related questions you might consider:

1. What is the difference between $\subset$ and $\subseteq$?
2. Can a set be a subset of itself if it is not empty?
3. What is the power set of the empty set?
4. How do you prove that any set is a subset of itself?
5. What does it mean for one set to be a proper subset of another?

Tip: When working with set theory, always remember that an empty set is a subset of every set, including itself.