A cylinder with both ends the same position in space is not a disc but a
degenereate cylinder.
I've gotten this one. I'm pretty sure a box with the same two vectors will
also generate the degenerate error.

A smooth triangle with opposing normals is something different, I think. But
it still won't render.

Josh
Warp wrote:

>   About a recent post in p.general:
>
>   When is a triangle degenerate?
>   I think that one case is when two of the vertices or all the three are
> actually the same point. In this case it would be just an infinitely thin
> line or point.
>   I faintly remember that povray also considers denerate a smooth triangle
> with the vertex normals pointing to different sides of the triangle. Is
> this so?
>   Any other case?
>
> --
> main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
> ):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

--
Josh English
eng### [at] spiritonecom
"May your hopes, dreams, and plans not be destroyed by a few zeros."

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