Polyhedron_base1.an_affine_basis: Update documentation

src/sage/geometry/polyhedron/base1.py

@@ -426,7 +426,7 @@ def ambient_dim(self):
 
  def an_affine_basis(self):
  """
- Return points in ``self`` that are a basis for the affine span of the polytope.
+ Return points in ``self`` that form a basis for the affine span of ``self``.
 
  This implementation of the method :meth:`ConvexSet_base.an_affine_basis`
  for polytopes guarantees the following:
@@ -438,6 +438,9 @@ def an_affine_basis(self):
  one vertex that is in the difference. Thus this method
  is independent of the concrete realization of the polytope.
 
+ For unbounded polyhedra, the result may contain arbitrary points of ``self``,
+ not just vertices.
+
  EXAMPLES::
 
  sage: P = polytopes.cube()
@@ -455,8 +458,7 @@ def an_affine_basis(self):
  A vertex at (4, 1, 3, 5, 2),
  A vertex at (4, 2, 5, 3, 1)]
 
- For unbounded polyhedra, the result may contain arbitrary points of ``self``,
- not just vertices::
+ Unbounded polyhedra::
 
  sage: p = Polyhedron(vertices=[(0, 0)], rays=[(1,0), (0,1)])
  sage: p.an_affine_basis()