You take one very large mirror and hang it to form an arm, then hang two more mirrors perpendicular to it to form an L-shape.

想象一下，你有一块很大的镜子，把它作为一条边，然后用另外两块镜子与它垂直放置作为另一条边。

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In one mirror was drawn a stick arm with a hand pointing west.

在一面镜子上画有一只伸直的胳膊，手指向西边。

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Back in his cell, Michael stands with his arm out the front doors, using a mirror to check the location of the guards.

Michael站在牢房内，将手伸出牢房门外，托起一面小镜子查看警卫的位置。

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In the mirror her reflection playfully swept out her arm.

NEWYORKER: Miracle Polish

"It is a spatial reasoning task for the robot to understand that its arm is on it not on the other side of the mirror, " Justin Hart, the PhD student leading the research told BBC News.

BBC: Robot learns to recognise itself in mirror

So far the robot has been programmed to recognise a reflection of its arm, but ultimately Mr Hart wants it to pass the "full mirror test".

BBC: Robot learns to recognise itself in mirror