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For this one, you may have to put your "Visualizing Hat" on, but bear with me. Imagine that you are in a square room, no bigger than 2m squared. You cannot see the ceiling, because there is a heavy stone that runs to the edges of the room, along tracks in each corner. You can try to push it up, or let it slide down, but you cannot put move it off your shoulders. You're stuck. It's dark. And, unfortunately for you, it's your fault that you're in this situation. If you keep the stone on your shoulders, you can reach out to the wall. You can feel the handle of a door, but it is locked. It needs a key. And, it can only be opened from the outsid