def METHOD_NAME(vk: str, action: str, position: bool, arg: Any=None):
    assert vk in S['members'], 'Not a member.'
    assert action in [INTRODUCE_MOTION, VOTE_ON_MOTION], 'Invalid action.'
    if action == INTRODUCE_MOTION:
        assert S['current_motion'] == NO_MOTION, 'Already in motion.'
        assert 0 < position <= REMOVE_SEAT, 'Invalid motion.'
        if position == REMOVE_MEMBER:
            assert_vk_is_valid(arg)
    elif action == VOTE_ON_MOTION:
        assert type(position) == bool, 'Invalid position'