The Solution Of The Double Dummy Problem: How should we make the 6H Contract:

The solution is a grand coup, a rarely and nice endplay. Let's see, how should we do that.

The opening lead is the ten of spades, because North's 2♣ bid was natural, game forcing.

Now, we have to lose a diamond, and we cannot make the contract without the diamonds. The other suits are more or less ok for us.

Therefore we should win the 1st trick in the hand, in order to have a rantree in spades to the dummy, we should play a small heart to the dummy's King.

Unfortunately, West has a void in hearts.

Now we should play a diamond from the dummy. East must put the Queen of diamond, otherwise we make the contract easily, crosruffing the hand.

We win East's diamond honor with the Ace and we should continue with the Jack of diamonds from the hand. We can see, that the 9 comes from West, and we can count now, that East seems to have also 4 diamonds nearby his 5 cards in hearts.

Now, if we are lucky enough, that he has at least 2 spades and a club in his hand, we can win our contract.

East should try to destroy our communication between the hand and the dummy, but we have 2 black top tricks at the dummy and he cannot destroy both.

Let's assume that East plays the Jack of spades after winning the King of diamonds. (it is simmetric with the club continue.)

Now we play our small heart from the dummy, East cannot put the Jack, so we win it with the nine of hearts in the hand.

Now we play the ten of diamonds from the hand, and we see, that East really has 4 diamonds in his hand, when West discards a spade to our ten of diamonds.

We can also play the eight of diamonds as a trick from the hand.

The last 5 cards endplay looks like this:

We have to go to the dummy with the Ace of clubs, we have to make a ruff to equal our heart length with East,

At trick 11, we ruff our bad diamond with the Queen of hearts, East has to underruff, because he has only hearts in his hand.

At the 12th trick we play any card from the dummy, and finesse the Jack of hearts in East's hand.

Nice hand. Please recognize, that if you play the King of spades in trick 1, in order to play the 1st diamond finess, the hand is already misplayed, because East can cut you from the dummy, if he plays the nine of clubs after the King of diamonds.