-Samples of expressions
-
-The *lambda* calculus has an associated proof theory. For now, we can regard the proof theory as having just one rule, called the rule of **beta-reduction** or "beta-contraction". Suppose you have some expression of the form:
+Examples of expressions:
+
+<blockquote><code>
+x<p>
+(y x)<p>
+(x x)<p>
+(\x y)<p>
+(\x x)<p>
+(\x (\y x))<p>
+(x (\x x))<p>
+((\x (x x)) (\x (x x)))<p>
+</code></blockquote>
+
+The lambda calculus has an associated proof theory. For now, we can regard the
+proof theory as having just one rule, called the rule of **beta-reduction** or
+"beta-contraction". Suppose you have some expression of the form: