finitions in
Listing 15-25. This code creates a list in `a` and a list in `b` that points to
the list in `a`. Then it modifies the list in `a` to point to `b`, creating a
reference cycle. There are `println!` statements along the way to show what the
reference counts are at various points in this process.
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<p>リスト15-26でリスト15-25の定義を使用する<code>main</code>関数を追加しています。このコードは、<code>a</code>にリストを、
<code>b</code>に<code>a</code>のリ�