# edge_list not working with IndexFaceSet

Considering for example,

```
pl=implicit_plot3d((lambda x,y,z: x^2+y^2+z^2-1),
(x,-1,1),(y,-1,1),(z,-1,1), plot_points=[10,10,10])
pl.triangulate()
```

Then,

`pl.vertex_list()`

returns the vertex list and`pl.index_faces()`

also works perfectly and returns the triangular faces.

However, `pl.edge_list()`

gives the following error:

```
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-388-05ccc951c815> in <module>
----> 1 st.edge_list()
.. site-packages/sage/plot/plot3d/index_face_set.pyx in sage.plot.plot3d.index_face_set.IndexFaceSet.edge_list (build/cythonized/sage/plot/plot3d/index_face_set.c:9602)()
745 ((1.0, -2.0, 3.0), (1.0, 2.0, 3.0))
746 """
--> 747 return list(self.edges())
748
749 def vertices(self):
.. /site-packages/sage/plot/plot3d/index_face_set.pyx in sage.plot.plot3d.index_face_set.IndexFaceSet.edges (build/cythonized/sage/plot/plot3d/index_face_set.c:9522)()
732 ((1.0, -2.0, 3.0), (1.0, 2.0, 3.0))
733 """
--> 734 return EdgeIter(self)
735
736 def edge_list(self):
... site-packages/sage/plot/plot3d/index_face_set.pyx in sage.plot.plot3d.index_face_set.EdgeIter.__init__ (build/cythonized/sage/plot/plot3d/index_face_set.c:21418)()
1735 self.set = face_set
1736 if not self.set.enclosed:
-> 1737 raise TypeError("Must be closed to use the simple iterator.")
1738 self.i = 0
1739 self.j = 0
TypeError: Must be closed to use the simple iterator.
```