Another interesting system hand for me from the Bermuda Bowl Finals.
I like to open 1D as an unbalanced opening, meaning 6+ diamonds, or 4+ if also holding a stiff or void on the side. After almost 20 years playing this way, I believe that the benefits in the 1D sequences outweighs some of the possible ambiguities of 1C sequences. Actually, the ambiguities of 1C sequences often helps, in creating more difficult lead problems for the opponents.
So, Opener starts 1D. As the diamonds are 4-card in length, Opener must have a stiff or void.
Responder has an easy response. He knows that this is Opener's stiff, most likely. Still, 1S.
Opener can now rebid 1NT. Unlike in standard, where we are loath to rebid 1NT with a stiff in partner's suit, 1NT here promises a stiff in partner's suit, easing the pain. Liability into an asset, and all that.
Responder now bids 2D, GF and artificial.
Opener shows the heart suit by bidding 2H. Strangely, perhaps, for some, he also denies that his stiff spade is an honor. Opener actually would be able to rebid 2S, instead, if his stiff spade had been an honor.
Responder suggests clubs, 3C.
Opener agrees, as he has a maximum and primes. 3D (two of the top three honors).
Responder continues with 3H (one top heart honor).
Opener has already denied a spade honor, so 3S would not show one top spade. The only question is "stiff or void?" Lacking void, he bypasses that. He might think of bidding 3NT. His 3NT bid would seem to deny (1) ability to show two top clubs (4C), (2) ability to show a third top diamond (4D), and (3) enough info to start the Ace-asking sequence. It is the last meaning that is troubling. His hand so far is relatively under-described, and he has a great hand.
The solution is to reconsider that 3NT would be "non-serious" in implication. Thus, any call above 3NT is "serious." He may therefore make a Last Train bid. 4H seems right. This sounds like Last Train, because hearts is technically somewhat "in focus," such that 4S would be RKCB for diamonds. That would be my call if the partnership was very well tuned. If not, I suppose I'd bid 4C and hope that partner realized the pinch here -- no way to cue hearts.
Anyway, Responder will quickly, after asking for Aces, realize that Opener has x-Axxx-A(K/Q)xx-Axxx, and he can ask for the diamond situation if he wants.