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To this two-dimensional sphere-universe there is a

three-dimensional analogy, namely, the three-dimensional

spherical space which was discovered by Riemann. its points are

likewise all equivalent. It possesses a finite volume, which is

determined by its "radius" (2π2R3). Is it possible to imagine a

spherical space? To imagine a space means nothing else than that

we imagine an epitome of our "space" experience, i.e. of

experience that we can have in the movement of "rigid" bodies. In

this sense we can imagine a spherical space.