Use $\subseteq$ or $\nsubseteq$ in the blank to make a true statement. $\{d, e, i\}$ $\{d, d, e, e, i, i\}$ $\subseteq$ $\nsubseteq$

Step 1 ：The question is asking whether the set $\{d, e, i\}$ is a subset of the set $\{d, d, e, e, i, i\}$.

Step 2 ：In set theory, a set A is a subset of a set B if every element of A is also an element of B.

Step 3 ：The repetition of elements in a set does not change the set itself, because sets are collections of distinct objects.

Step 4 ：Therefore, the set $\{d, d, e, e, i, i\}$ is actually the same as the set $\{d, e, i\}$.

Step 5 ：So, the set $\{d, e, i\}$ is a subset of the set $\{d, d, e, e, i, i\}$.

Step 6 ：Final Answer: $\boxed{\subseteq}$