作为课后作业，我们需要证明以下命题：如果灯过去是关着的，并且现在它是开着的，请证明有人按了开关我真的试着证明它了。我花了许多小时，试图证明这个命题。

For our homework, we had to prove the converse: if the light was off, and it's on now, prove that you flipped it.

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我正在做作业，突然所有的灯都熄灭了。

I was doing my homework, suddenly all the lights went off.

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我刚做完作业，突然灯全灭了。

I had just finished my homework when all the lights went out.

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