Posted 2015-January-25, 18:49
South's 5 ♦ bid just isn't right.
One thing I harp about when a player is considering slam is for each player to ask "What do I need to know to insure slam has a reasonable play?". Here, South's answer to that question is simple -- "I need to know at a minimum that we don't have two ♣ losers." By bidding 5 ♦, South makes it impossible for North to show a 2nd round ♣ control below slam.
Indeed, a case could be made that 5 ♦ shows a ♣ control along with the ♦ A. I think that's what the robot took the bid as meaning.
If 4 NT wouldn't be taken as a form of Blackwood, then that would be the best bid. Years back we called it DI (Declarative Interogatory) 4 NT. It shows interest in slam and asks if partner has anything else to show. In this case, it denies the ♣ A. With that card, South could simply continue cueing by bidding 5 ♣.
If 4 NT would be a form of a Blackwood, then South is constrained to bidding some number of ♠s. In any case, South can't use Blackwood with the actual hand because it doesn't get the right info from North. 4 ♠ can't completely be a signoff. From what North can see, even if South held ♥ KQJ and ♦ AKQJ, a black suit A must be held to get to the normal 20-21 for the 2 NT bid. If South bids 5 ♠ would North necessarily recognize that it asks about a ♣ control? Even North if does, could North's hand be something like ♠ J109xx ♥ AQxx ♦ x ♣ QJx where 5 ♠ isn't completely assured. 4 ♠ also might let North use Blackwood when its right to do so.
One little wrinkle might be considered once ♠s are set by the 3 ♠ call after Smolen. 3 NT shouldn't be a logical contract anymore. So 3 NT could be used to begin cueing and deny a ♣ 1st round control. Continuing with 4 ♦ (1st in ♦, no 1st in ♣), 4 ♥ (1st in ♥), the ♣ control issue comes more clearly into view while saving some bidding space.