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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晚上，上了一天的课，还要为同学们改作业本，每想起老师，就仿佛看见老师窗前那盏长明的灯。

Evening, top the lesson for a day, return want for the classmates change homework origin, each remind of teacher, imitate fo to see a teacher before the window that to grow a clear light.

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