Imports a NFA from a JSON file.

    :param str input_file: path+filename to JSON file;
    :return: *(dict)* representing a NFA.

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