How to make pictures using raytracing with povray: in-class project 1
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1. Create a three-dimensional cross of cylinders along the coordinate axes.
   That is: three cylinders, of the same radius, going in x,y,z direction.

2. Take points <1,0,0>, <-1,0,0>, <0,1,0>, <0,-1,0>, <0,0,1>, <0,0,-1>,
   and connect any two of them but tose that are diametral by a cylinder.
   Then place around each of these six points a small ball.
   This gives an octahedron (also called crosspolytope).

3. In the same way, make a cube.

4. Take every second vertex ov the cube, so along each edge only one, and 
   connect them. This gives a regular tetrahedron.