🚧 Setup for 6.1

chapter_6/test_yourself.md

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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, _____.