Here is its syntax:
<blockquote>
-**Variables**: `x`, `y`, `z`, ...
+<strong>Variables</strong>: <code>x</code>, <code>y</code>, <code>z</code>...
</blockquote>
Each variable is an expression. For any expressions M and N and variable a, the following are also expressions:
<blockquote>
-**Abstract**: <code>(λa M)</code>
+<strong>Abstract</strong>: <code>(λa M)</code>
</blockquote>
We'll tend to write <code>(λa M)</code> as just `( \a M )`.
<blockquote>
-**Application**: `(M N)`
+<strong>Application</strong>: <code>(M N)</code>
</blockquote>
Some authors reserve the term "term" for just variables and abstracts. We won't participate in that convention; we'll probably just say "term" and "expression" indiscriminately for expressions of any of these three forms.