A boy is looking up at the sky and sees something
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A boy is looking up at the sky and sees something, but he doesn't know what it is. He asks his mother but she can't tell so she points him to his brother. But again his brother has no idea, so he points him to his father. Finally the boy asks his father, but his father has no idea either. So his father points him back to his mother.
At this point the boy knows what it is, because it takes 3 points to define a plane.