def convert_toptica_boolean(response):
    """
    Converts the toptica boolean expression to a boolean
    :param response: response string
    :type response: str
    :return: the converted boolean
    :rtype: bool
    """
    if response.find('Error: -3') > -1:
        return None
    elif response.find('f') > -1:
        return False
    elif response.find('t') > -1:
        return True
    else:
        raise ValueError('cannot convert: ' + str(response) + ' to boolean')
