At the table, West bid 3NT. North led the jack of diamonds,
and declarer was down one, losing four diamond tricks and
the ace of clubs.

The correct rebid by West is 2, fourth-suit forcing. West
knows that the final contract will probably be 3NT, but with
ace-third of the unbid suit, he should attempt to get his
partner to become declarer, in case his partner holds the
queen. With South on lead, 3NT is not only unbeatable,
but declarer makes at least 11 tricks!