el conforming to <code><a href="Protocols/Differentiable.html">Differentiable</a></code> for diffing from other sections:</p>
<pre class="highlight swift"><code><span class="kd">enum</span> <span class="kt">Model</span><span class="p">:</span> <span class="kt">Differentiable</span> <span class="p">{</span>
    <span class="k">case</span> <span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">,</span> <span class="n">c</span>
<span class="p">}</span>

<span class="k">let</sp