If any of these points are connected to each other, then we have found a triangle of three mutual friends.

如果这些点相互连接，我们得到一个三角形，有三对人互为朋友。

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If any of these points are connected to each other, then we have found a triangle of three mutual friends. (these two points are connected, plus they are both connected to the original point).

如果这些点相互连接，我们得到一个三角形，有三对人互为朋友。(四个点中的两个点相连，加上它们又都与最初的一个点相连)。

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If any of these points are not connected to each other, then we have found a triangle of three mutual strangers.

由此，我们得到一个互为陌生人的三角形。

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In fact, the hypotenuse is a line between two angles, so what is wrong with a fourth person being the hypotenuse between two of the three people who are presumably at the points of the triangle?

ECONOMIST: Letters