code: def _delta(self, graph, cur_state, char):
          
          for arc in cur_state.arcs:
              if graph.isyms.find(arc.ilabel) == char:
                  return graph[arc.nextstate]
          return None
docs: Args:
              graph (Fst Acceptor): The DFA
              cur_state (Fst State): The current State
              char (Char): The input character
          Returns:
              (Fst State): The destination state