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**Test Yourself**

1. The notation $A \subseteq B$ is read "_____" and means that _____.

2. To use an element argument for proving that a set $X$ is a subset of a set
   $Y$, you suppose that _____ and show that _____.

3. To disprove that a set $X$ is a subset of a set $Y$, you show that there is
   _____.

4. An element $x$ is in $A \cup B$ if, and only if, _____.

5. An element $x$ is in $A \cap B$ if, and only if, _____.

6. An element $x$ is in $B - A$ if, and only if, _____.

7. An element $x$ is in $A^c$ if, and only if, _____.

8. The empty set is a set with _____.

9. The power set of a set $A$ is _____.

10. Sets $A$ and $B$ are disjoint if, and only if, _____.

11. A collection of nonempty sets $A_1, A_2, A_3, \dots$ is a partition of a set
    $A$ if, and only if, _____.