System observability is examined and two necessary conditions for the system to be observable are obtained.

首先分析了系统的观测性，得出了系统可观测的两个必要条件。

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On the basis of light interaction with two-level atomic system, we derive the interaction solitary wave equations, its solution and two necessary conditions for the existence of the solution.

在光与二能级原子系统相互作用的基础上，我们导出相互作用孤立波方程组及其精确解，以及存在解的两个必要条件。

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The two countries should continue to drastically reduce their nuclear arsenals so as to create necessary conditions for the eventual complete and thorough nuclear disarmament.

两国应继续大幅削减核武库，为最终全面、彻底核裁军创造必要条件。

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Here, Mr Draghi was very clear that "monetary policy remains independent": conditions one and two are necessary for the ECB to act, but there's no guarantee that it will.

BBC: Draghi will do what it takes (give or take)

They said the two countries, which joined the EU in 2007, had met the conditions necessary for applying Schengen rules efficiently.

BBC: EU warned against changing Schengen deal on borders