协变和逆变的区别对于张量的计算尤为重要，这往往会出现混合方差。

The distinction between covariance and contravariance is important for computations with tensors, which often have mixed variance.

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通过把高阶张量写成若干逆变和协变矢量的乘积，直接从变换入手，给出了定义高阶张量协变导数的另一种方法。

This paper discusses another way, which is rewritten as product of a few contravariant vectors and covariant vectors, to define higher order tensors covariant derivative through transformations.

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