positive series的用法和样例：
例句
- The process of replacing polynomials by formal power series is an example of a general device known as completion.
用形式幂级数来代替多项式的过程是被称之为完备化的这种一般手段的一个例子。 - To terminate a computational process in accordance with some rule, e.g., to end the evaluation of a power series at a specified term.
根据某种规则终止一个计算过程，例如，对幂级数估值时，取到指定项就停止运算。
