cube 
* Cube of side 2 centred at the origin
* Borrowed from:
* http://cgm.cs.mcgill.ca/~avis/C/lrslib/USERGUIDE.html
H-representation 
begin 
6 4 rational 
1 1 0 0 
1 0 1 0 
1 0 0 1 
1 -1 0 0 
1 0 -1 0 
1 0 0 -1 
end