'>fold</span>(<span class='number'>0</span>, <span class='op'>|</span><span class='ident'>old</span>, <span class='ident'>new</span><span class='op'>|</span> <span class='ident'>old</span> <span class='op'>^</span> <span class='ident'>new</span>)
});</pre>

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<p>もう一つの方法としては、ジェネリ�