docs: def nfa_json_importer(input_file: str) -> dict:
      """ Imports a NFA from a JSON file.
  
      :param str input_file: path+filename to JSON file;
      :return: *(dict)* representing a NFA.
      """
      file = open(input_file)
      json_file = json.load(file)
  
      transitions = {}  # key [state in states, action in alphabet]
      #                   value [Set of arriving states in states]
      for p in json_file['transitions']:
          transitions.setdefault((p[0], p[1]), set()).add(p[2])
  
      nfa = {
          'alphabet': set(json_file['alphabet']),
          'states': set(json_file['states']),
          'initial_states': set(json_file['initial_states']),
          'accepting_states': set(json_file['accepting_states']),
          'transitions': transitions
      }
  
      return nfa