Hands are from the San Diego Unit Game, October 7, 2018.
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West: ♠KQ85 ♥QJ1072 ♦A95 ♣9
East: ♠A106432 ♥A ♦Q10 ♣K762
East opens 1♠ in second seat. Partner splinters to 4♣—showing four card trump support, and a singleton or void in clubs. The usual rule is to subtract any secondary honors (anything other than the Ace) in the splinter suit. If you still have an opening hand, look for slam. Otherwise sign off. However, I liked the East hand even with the wasted the ♣K. My logic was that partner is very likely to have the ♠K on this auction, in which case we don't have any spade losers with normal breaks. If partner has the ♦AK, we will be gin for 6♠. (Or, if partner has ♦AJx, we may need a finesse.) So, I cue-bid 4♥ to show a control (and deny first OR second round diamond control). Partner cue bid 5♦. Going past 4NT implies he is not worried about our trump suit, so I am assuming now he has the King AND Queen of trumps along with the ♦A. So, I bid 5♥ to show second round control of hearts and partner put me in 6♠.
We got the favorable lead of the ♣A (not unreasonable on this auction) and a club continuation. You must develop the hearts in order to discard a diamond loser. It appears that LHO has the ♦K since you did NOT get a diamond lead, nor was there a lead-directing double when partner cue-bid diamonds originally. So, the ♥K is a bit more likely to be on your right, but you don't have to put all your eggs in that basket yet.
Win the club continuation with the ♣K, discarding a diamond from Dummy. Unblock the ♥A. Play a middle spade to Dummy's ♠K. Both defenders follow. Now play a low heart and ruff it with the ♠A. Both opponents follow. Middle spade over to the ♠Q, pulling the last trump as RHO discards a diamond. Play third round of hearts and ruff it. LHO shows out. Ruff a club to Dummy. NOW take the ruffing finesse against RHO's the ♥K, promoting the ♥J. Ruff last club on Dummy. Discard losing diamond on good heart. You still have a trump left in your hand to ruff Dummy's losing diamond.
Without the favorable the ♣A lead, you would have to take the ruffing finesse in hearts from the beginning. Although hearts are 5-2, the favorable drop of the ♥98 doubleton in hearts means that Dummy's the ♥7 will be a winner. On that scenario, you get four heart tricks, six spade tricks, the ♦A and a club ruff in Dummy.
South: ♠AQ3 ♥A ♦A62 ♣A97654
North: ♠KJ8 ♥KQ953 ♦Q53 ♣K3
A number of N/S pairs missed this slam.
My suggested 2/1 sequence is 1♥ by North; 2♣ by South (establishing a game force); 2NT by North; 3♣ by South (showing either a mild slam try in clubs; or perhaps some uneasiness about no trump; or just seeking more information). 3NT by North. 4NT (quantitative raise) by South. North, with a full 14 HCP, should accept the invite to 6NT. Plus, the ♣K should be golden on this auction, filling in partner's 6-card suit.
Since the opening leader has the ♦K, s/he cannot safely lead a diamond. (Declarer would be forced to let it run to her the ♦Q.) So, Declarer has time to give up one club trick to establish five club tricks and has three spade tricks, three heart tricks, and one diamond trick on sheer power.