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This is an oriented surface (with two sides), bounded by the trefoil, viewed from above. |
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The same surface, now viewed from the side. Indeed, it has two sides. Still, its structure is somewhat hard to grasp. Note that the surface is threefold symmetric. Each band from the bottom to the top is similar. |
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This is a more structural view. The surface consists of two disks,
connected by twisted bands. The knot is still a trefoil. We can
distort it whatever we want, as long as we don't cut it and do no pass
the string through itself. Click here for the next puzzle... |