�を使用するように<code>main</code>を更新します:</p>
<!--
<span class="filename">Filename: src/main.rs</span>
-->
<p><span class="filename">ファイル名: src/main.rs</span></p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">use std::rc::{Rc, Weak};
</span><span class="boring">use std::cell::RefCell;
</span><span class="boring">
</span><span class="boring">#[derive(Debug)]
</span><span class="boring">struct Node {
</span><span class="boring">    value: i32,
</sp