和以前一样，它来源于这样一个事实，混合二阶导数，求导次序改变，结果不变。

And, as before, this comes from the fact that the mixed second derivatives are the same, no matter in which order you take them.

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我会遵循本文中的大多数(但不是全部)步骤，而且我会改变一些步骤的次序。

I will follow most, but not all, of these steps in this article, and I will change the sequence somewhat.

youdao

软件维护被基本的敏捷概念所包裹：从优先考虑的候选库中开始工作，或者改变次序，并且交付工作软件的增量发布。

Software maintenance is framed by fundamental Agile concepts: working from a backlog of prioritized tickets or engineering change orders, and delivering incremental releases of working software.

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