🚧 Setup for 4.1

chapter_4/test_yourself.md

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+**Test Yourself**
+
+Page 194
+
+1. An integer is even if, and only if, ______.
+
+2. An integer is odd if, and only if, ______.
+
+3. An integer $n$ is prime if, and only if, ______.
+
+4. The most common way to disprove a universal statement is to find ______.
+
+5. According to the method of generalizing from the generic particular, to show
+   that every element of a set satisfies a certain property, suppose $x$ is a
+   ______, and show that ______.
+
+6. To use the method of direct proof to prove a statement of the form, "For
+   every $x$ in a set $D$, if $P(x)$ then $Q(x)$," one supposes that ______ and
+   one shows that ______.