@pimms.value<EOL><INDENT>def edge_faces(edges, edge_face_index):<DEDENT>
return tuple([edge_face_index[e] for e in zip(*edges)])<EOL>
tess.edge_faces is a tuple that contains one element per edge; each element
tess.edge_faces[i] is a tuple of the 1 or two face indices of the faces that contain the
edge with edge index i.