They take place in a curve.You express everything in terms of one variable and after substituting, you end up with a usual one variable integral that you know how to evaluate.

它们产生在一条曲线上，任何的积分都可以只用一个变量来表示，进行变量替换后，你得到一个，我们知道怎样计算的，单变量积分。

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Increased use of XML is prompting many companies to evaluate how their databases can be adapted to cope with the complex, highly variable structures inherent in many XML messages and documents.

XML的广泛使用促使许多公司评估自己的数据库如何应对大量XML消息和文档中复杂的高度可变的结构。

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The running program will evaluate the expression in Listing 1 twice, with the $exp variable set to and .

运行的程序将对清单 1 中的表达式进行二次求值，其中 $exp 变量分别被设置为 和 。

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