Neil Cohen, an old friend of mine, sent in this deal from a robot game at Bridge Base Online (bridgebase.com). As North, he improvised a negative double of three hearts. The robots define this call as promising four or more spades, hence South’s offbeat four-spade call.
One of the more charming features of the robot game is that you can never be dummy; if partner wins the auction, you switch seats to declare the deal. Thus, no matter how sticky a mess the machine has landed you in, you are the one to bear the brunt!
Here, Cohen had to declare the “super Moysian” 3-3 fit on the favorable defense of the diamond ace lead followed by a heart shift and a diamond return. It was easy from there, with Cohen able to draw trumps and run clubs. West could take his trump trick at his leisure.
The weird diamond lead effectively surrendered control. Say, however, West leads a heart instead, East winning and returning the suit. Declarer cannot draw trumps now without conceding the hearts, so he starts to run clubs.
If West ruffs in and plays a heart, declarer ruffs in hand, draws trumps and runs clubs, making three spades, a heart, a ruff and five clubs. A trump return is no better; declarer can just knock out the diamond ace before pulling trumps.
If West chooses to discard on the first three clubs, declarer ends in hand and leads a diamond up. West again has no winning defense.
Only an initial trump lead beats the contract. Details left to the interested reader.