-> Simple objects to implement
* Polyhedron

-> Methods to implement (for all objects)
* Scale
* Mirror
* Homogeneous transformation (matrix)

-> Operations to implement:

BUGS:
 - The operation   obj = obj + something; does not work well

-> Function to implement(for all objects)
* Dimension control: check that all paramters introduced by user have a valid (geomatrically speaking) value.