'Return list mapping each vertex index to a list of face indexes that use the vertex.'

def vertexFaces(self):

    if (self._vertexFaces is None):
        self._vertexFaces = [[] for i in xrange(len(self.vertexes()))]
        for i in xrange(self._faces.shape[0]):
            face = self._faces[i]
            for ind in face:
                self._vertexFaces[ind].append(i)
    return self._vertexFaces
