这个一般读作，而不读作倒三角，或者别的，它是一个算子的符号。

Del so, this guy usually pronounced as del, rather than as pointy triangle going downwards or something like that, it's a symbolic notation for an operator.

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这个是符号化的向量算子，其中它的分量是偏微分算子。

That was this symbolic vector operator in which the components are the partial derivative operators.

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第一部分简单介绍了本文所涉及到的一些基本定理、符号、概念，以及一些与正线性算子有关的成果。

In the first part, some fundamental theorem, symbol, concept are introduced, including some valuable results on linear positive operators.

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