traction. All the <em>free ocurrences</em> of <code>x</code> in <code>e</code> become <em>bound</em> by the abstraction.</p>
<p>To see that the abstraction above represents the identity function, we can apply it to some value:</p>
<pre><code class="language-clojure">((fn [x] x) 42)
;=&gt; 42
</code></pre>
<p>We just encountered two other major ingredients of the lambda-calculus:</p>
<ul>
<li>
<p>an <strong>application</strong> <code>(f e)</code> of a function <code>f</code> to lambda-term <code>e</code></p>