| Construct the spiral as thus: |
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The stereographic projection from the xy plane to the unit
sphere is given by
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| Construct three cylinders with any two touching at one point. |
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| Construct one-half of the tangent cone to a sphere. |
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| Construct one-half of a right solid cylinder whose boundary consists of the helicoid, part of the cylinder and two semi-disks. |
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| Construct the cyclide by inverting a torus. |
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