1. One notrump. Though it is normal to raise partner whenever you have four trumps — and it might therefore be contended that the proper rebid is two diamonds — there are several good reasons for preferring one notrump.
First, the hand is well-suited for notrump play, which is best expressed by a rebid of one notrump. A two-diamond bid would tend to imply more in the way of distributional values, such as a singleton or a couple of doubletons, which is not the case here.
Also, the opponents’ silence makes it more likely that partner has a good hand and is headed for game. If this hope materializes, a nine-trick notrump game seems far more promising than an 11-trick diamond game. Furthermore, if the best contract is notrump, your holdings in the majors suggest that the hand will play better from your side of the table.
2. Three notrump. You should be unwilling to settle for less than three notrump once partner responds with one diamond. A jump to two notrump or three clubs would run the risk of a pass, since either of these bids would merely invite, but not force, partner to bid again.
3. Two hearts. The jump-shift in hearts forces partner to bid again and commits the partnership to game. With this gigantic hand, you can afford to insist on another response, even though partner might have only six points. Game, or perhaps even a slam, is highly probable in clubs, diamonds, hearts or notrump, but which denomination and how far to go remains to be resolved.
4. One spade. You have no choice but to try to describe your distribution on an installment-plan basis, bidding spades now and showing your club length and diamond support later to identify the three-suited nature of your hand. Of course, you have a strong preference for clubs as trumps over spades, but at this stage you cannot afford to bypass the possibility that partner has four-card spade support.
5. Four notrump. The number of aces partner has is the key to how many tricks you can make with diamonds as trumps, so you invoke Blackwood. If partner shows no aces by bidding five clubs, you next bid five diamonds; if he shows one ace, you bid six diamonds; if he shows two aces, you bid seven diamonds.
Tomorrow: South has a problem to solve.