Each vertex of a parameterized polyhedron is an affine function of the
parameters , defined over a *validity domain*: each vertex
exists only if is included into the validity domain associated to
this vertex. There are two ways of representing such a set of
parameterized vertices and validity domains:

- as a list of pairs, each one containing a vertex and its validity domain,
- as a list of distinct validity domains, and the complete matrix associated to each validity domain.

Sorin Olaru 2002-04-24