Hirsch bound for H-polyhedra with at most three excess rows

Let P be a bounded H-polyhedron in ambient R^d described by n real linear inequalities. If n is at most d+3, then its padded vertex-edge graph diameter is at most n-d (natural subtraction). The description may have redundant inequalities or zero normals, and P may be empty or lower dimensional. No strict feasibility or irredundancy is assumed. In particular, at most two excess describing rows gives diameter at most two. This is the classical small-excess consequence of low-dimensional Hirsch, not a uniform polynomial bound for arbitrary excess.