code: def extender(self, edge):
          "See what edges can be extended by this edge."
          (j, k, B, _, _) = edge
          for (i, j, A, alpha, B1b) in self.chart[j]:
              if B1b and B == B1b[0]:
                  self.add_edge([i, k, A, alpha + [edge], B1b[1:]]f extender(self, edge):
          "See what edges can be extended by this edge."
          (j, k, B, _, _) = edge
          for (i, j, A, alpha, B1b) in self.chart[j]:
              if B1b and B == B1b[0]:
                  self.add_edge([i, k, A, alpha + [edge], B1b[1:]])
docs: See what edges can be extended by this edge.