Answer: Bridge Problem 3

South must win the ♠A, take two top trumps in dummy, cash the ♦AK and ruff a diamond, return to hand with the heart king, and draw the last round of trump (they break). Now a spade play puts East on lead with nothing but spades left (if East ducks the spade, declarer has 11 tricks). When East plays another spade, South discards a heart from hand. Now the next spade from East can be ruffed by South and West is squeezed, having to give declarer the game-going trick in one of the red suits.

No other way of rectifying the count for the squeeze will work. Ducking a heart to West before trumps are drawn allows East to get a heart ruff. Ducking a heart to West after trumps are drawn — which means after the diamond ruff — allows West to cash the fourth diamond or play a heart, eliminating the last entry to dummy.