pi
or π (Pronounced as "pie".) An important number in geometry. This is defined to be the ratio of the circumference of a circle to the diameter of that circle, in flat space. π is an irrational number, which means that its exact value cannot be written down, though it can be calculated as precisely as necessary. Its value is approximately 3.14159265358979323...
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Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run twice as fast as that.