Polyhedra, facets and vertices

savecancel

I have a 6-dimensional, convex, compact polyhedron in $\mathbb{R}^{12}$, that I am calling P1. The polyhedron P1 was specified by giving a large number of inequalities. When I enter P1.faces(5) into Sage, I get the following

(A 5-dimensional face of a Polyhedron in RDF^12 defined as the convex hull of 6 vertices,
 A 5-dimensional face of a Polyhedron in RDF^12 defined as the convex hull of 7 vertices,
 A 5-dimensional face of a Polyhedron in RDF^12 defined as the convex hull of 7 vertices,
 A 6-dimensional face of a Polyhedron in RDF^12 defined as the convex hull of 7 vertices,
 A 5-dimensional face of a Polyhedron in RDF^12 defined as the convex hull of 6 vertices,
 A 6-dimensional face of a Polyhedron in RDF^12 defined as the convex hull of 8 vertices,
 ...)

How can there be two 6-dimensional faces, each with a different number of vertices, on the boundary of P1? I have checked that P1 really does have dimension 6.

Also, when I try to find a list of vertices on the boundary of any 5-dimensional face of P1, for example

P1.faces(5)[0].vertices_list()

I get an error message

AttributeError: 'tuple' object has no attribute 'vertices_list'

However, P1.faces(5)[0].vertices() works.

My second question is, how do I get a list of vertices on the boundary of an $n$-dimensional face?