void modify_vertex_position()
{
Polyhedron P;
Halfedge_handle h = P.make_tetrahedron();
if ( P.is_tetrahedron(h))
{
int i(0);
for(Vertex_iterator vi = P.vertices_begin(); vi != P.vertices_end(); ++vi,++i)
{
std::cout << "before changing vertex " << i << ": " << vi->point().x() << vi->point().y() << vi->point().z() << endl;
Point_3 pt(1, 0, 0);
vi->point() = pt;
std::cout << "after changing vertex " << i << ": " << vi->point().x() << vi->point().y() << vi->point().z() << endl;
}
}
}
