An Easy Problem?

On BBF, the following pair of hands was posted, with the question being whether anyone could avoid the trap of playing in 7♥. I thought this was somewhat interesting, in the solution, but incredibly easy, despite a number of convoluted sequences and "he should she should" analyses.

Opener: ♠ KQJxx ♥ xxxx ♦ A ♣ AJx
Responder: ♠ Ax ♥ AKQx ♦ KQx ♣ K10xx

The auction, 2/1 GF, started 1♠-P-2♣-P-2♥-P-3♥. Good start. At this point, however, the two auctions at two tables diverged, one Opener electing a 4♦ cuebid and the other 4♣. I don't get 4♦ at all. In the end, some guessing was required.

This seems so easy, though. But, there is a nice nuance late in the auction.

The obvious continuation seems to be for Opener to first cue his spades (3♠) to show two of the top three spade honors. Responder then bids 3NT serious. Opener can now cuebid 4♣. This should be enough for Responder to launch into RKCB.

After the 5♥ response (two, without), Opener can bid 5♠. Now, whatever agreements you have for 5♠, this leads to a nice call.

If 5♠ is a cheaper way of bidding specific Kings up-the-line, then Opener should bid 5NT to "show the King of spades." This shows something completely different, however. As Responder is making a grand slam probe, we must have all of the Aces. Therefore, Responder must have the spade Ace. If he has the spade Ace, then he knows that we have the spade King-Queen. Therefore, bidding 5NT to show the spade King would be redundant. It would be equally redundant to bid 5NT to show the spade Queen. Therefore, 5NT must show the unknown additional spade value of the spade Jack.

If 5♠ is an asking bid, asking for the spade King, then in this situation, for the same reason, 5♠ should be understood by both parties as actually asking for the spade Jack.

You will notice that this is a unique sequence, in that Opener, only because he lacks the spade Ace, knows from the grand slam try that 5NT shows the spade Jack, because Responder must have the spade Ace and must, therefore, already know about the top three spade honors. Otherwise, had Opener held the spade Ace, this nuance would not be known, and this 5♠ bid would be seeking the spade King (as opposed to the Queen). Responder should equally be in on this nuance.

In any event, look what Responder will now know. He will be able to count five rippers in the minors (diamond A-K-Q plus club A-K). He can count three heart tricks, now up to eight tricks. With the known four spade tricks (A-K-Q-J), he has 12 tricks, with three trick sources for a thirteenth -- spades coming in, hearts coming in, or something in clubs coming in -- plus all sorts of squeeze possibilities. The multiple options in three suits seems to clearly outweigh placing all of your eggs in the basket of hearts splitting 3-2 or partner having the Jack (and hearts not being 5-0), and no immediate spade or club ruff on opening lead.