基本的技能，像是减法、乘法和看时间等，通常是孩子会最先忘记的。

Basic skills, such as subtracting, multiplication and time-telling, are usually the first to go.

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本文介绍一种具有优先级扩展的时间自动机模型，并对一种计算d BM减法算法进行改进。

In this paper an extension of timed automata with priorities is introduced, and we present an improved algorithm to compute subtraction on DBMs.

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创建一个计算器类，能够在同一时间完成两个数字的加减法。不太懂，原文：%。

Create a class Calculator, which performs the addition and subtraction of two Numbers at a time. The sample code explains the expected API.

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