def METHOD_NAME(self) -> Set[str]:
    assert len(self._tx_acct_key_set)
    # All other accounts can be included into a lookup table
    acct_key_list = self._msg.account_keys[self._msg.header.num_required_signatures:]
    alt_acct_key_set = set([str(key) for key in acct_key_list if str(key) not in self._tx_acct_key_set])
    if len(alt_acct_key_set) + len(self._tx_acct_key_set) != len(self._msg.account_keys):
        raise ALTError('Found duplicates in the transaction account list')
    return alt_acct_key_set