[ggwhiz]

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Partner gets the wind in their sails after you open 4♠ and sets you down in 6 of them.

Opening lead, ♦K and yes, the ♥A is on your right as needed. The winning line is in the spoiler, not the one I found.

Spoiler

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You have to duck the opening lead. They return a mandatory trump (or it's over), you ruff out the ♥A and run all your trumps but one and west is beyond doomed.

It's a 5 card ending and they have to keep 2 diamonds and 3 clubs (or you can cross, pitch 1 and ruff 1 to set up the last) with the proper timing by virtue of the diamond entry intact.

[nige1]

Spoiler

ggwhiz says "Partner gets the wind in their sails after you open 4♠ and sets you down in 6 of them. Opening lead, ♦K and yes, the ♥A is on your right as needed. You have to duck the opening lead. They return a mandatory trump (or it's over), you ruff out the ♥A and run all your trumps but one and west is beyond doomed.It's a 5 card ending and they have to keep 2 diamonds and 3 clubs (or you can cross, pitch 1 and ruff 1 to set up the last) with the proper timing by virtue of the diamond entry intact."

Nice problem, ggwhiz! Amusingly, unless the opening lead is a ♣, you can make, double-dummy, even with the East-West hands beefed-up. For example, in this simplified set-up, Gib demonstrates that there is a double squeeze.in the red suits. After ruffing out ♥ and cashing all but one trump, you cross to the (now singleton) ♣A. To keep a diamond guard, a defender must throw a ♥, allowing you to set up a 2nd ♥ winner.

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