A K J 
          K 2 
          A K 
          A K Q J 10 9 
8 6 5                  Q 10 9 7 
Q J 10 9 8 7           6 5 4 
J 9 7                  Q 5 3 2 
7                      3 2 
         4 3 2 
         A 3 
         10 8 6 4 
         8 6 5 4 

East of course disputes the claim. The revoke is not established, so East is allowed to correct the revoke.

As far as I know, a headless chicken ruling from the books is that the defense is allowed to choose its play following a claim. It will choose to correct the revoke, which has not been established. It will then win the queen of spades and lead a heart, for down 4. This is inequitable because the defense committed the irregularity, yet the nonoffending side is being punished.

I think everyone agrees that this is an unequitable ruling and everyone tries to avoid it. Let me just comment for a moment on possible hands. It looks like this hand will go down 1 and anything which achieves down 1 is equitable. But the hand can be run as a pseudo-squeeze, forcing East to decide whether to protect diamonds or spades. And if West pitches a diamond, it is a real pseudo-squeeze. You may say that if West is a good player, West will not pitch diamonds. But most bridge players will not count hearts and hence will save a heart to protect against Axx in declarer's hand.

Also, in terms of equity, if the Jack and ten of diamonds are reversed, then there is a true squeeze. Declarer might read the situation, or guess right. Then down one is not equitable. Or the Queen-Jack of diamonds might drop doubleton, making the ten in hand good, and then down one is not equitable.

The equitable thing is that declarer should not lose whatever chance he had to make this slam without the revoke. And any questionable decisions should go against the offending side, which is the defense.

One reasonable ruling, in my opinion, is this. First, if and when East corrects the revoke, declarer will be allowed to change the card he played from hand following the revoke. This does declarer no good, I am just saying that this is the law. Now, he would also be allowed to change the card he led from dummy to the next trick, had he led a card from dummy before the revoke was established. Perhaps, as part of backing up the auction and allowing declarer to change his "play", declarer can be allowed to change his "claim".

Now, if declarer is allowed to change his claim, he is probably/reasonably allowed to change whether or not he claimed.

What if declarer has shown his hand? If defense is allowed to use this information, then declarer is still being punished for the defender's irregularity. Of course, declarer has also caused the problem by claiming. But there is a general principle here -- the nonoffending side should not be punished for reasonable actions it honestly takes in response to an unknown irregularity.

You can make declarer's hand UI to the defense, but that almost makes the hand unplayable. So it is reasonable to sort through the logical play of the hand without the infraction. In this case, there is a small chance that declarer will make seven. (West might save hearts if West does not count that declarer does not have a threat. If West pitches a diamond, then East is caught in a genuine squeeze, which declarer might read from East's discomfort. Or East might worry that declarer has the jack of diamonds. If it is a true squeeze, then defender's best hope is to bare the queen of spades. In addition to declarer guessing to drop the queen of spades, West might pitch all of his/her spades, forcing declarer to play for the drop.)

(Also, you can change the hand to give declarer the jack of diamonds. This gives declarer a choice of how to play the hand, one of which works. Another possibility is to give declarer the jack of diamonds and have the queen drop doubleton.)

So, I think it is reasonable to cancel the claim, if declarer wants to. He/she almost certainly will. If declarer has not shown his hand, then I suspect it would be okay to let play continue (but make the claim UI, just in case there is information in it). If declarer has shown his hand, then it is reasonable to try to imagine the hand.

One problem is this. Suppose that declarer has claimed, the revoke is corrected, and then declarer wishes to cancel claim but there is no legitimate bridge reason for changing the claim. Do you allow this? If you do, is declarer's hand still UI? If you have to play out the hand to resolve the claim (unlikely, but..), would you now resolve questions in favor of declarer?

What if the defender announces the revoke and declarer, upon hearing this, claims, knowing that he/she will be allowed to cancel it?

The impression I am trying to give is this. The lawmakers could address the problem of what to do when declarer claims after an unestablished revoke. But there are different situations. The laws could try to cover them all, but the result would be a lengthy section discussing a situation that most directors will never see.

In England

England has addressed this question. From their orange book: "A defender revokes, declarer claims, but the defender or his partner does not accept the claim. Acquiescence has not occurred and the revoke is not established by the claim. The Director allows the revoke to be corrected. He then determines the outcome of the claim, but, unlike a normal claim, doubtful points are determined against the revoker rather than against the claimer."

There are no doubtful points in this claim, so I think from this ruling declarer will be down 4. Of course, it is very doubtful that declarer would want to claim, and extremely doubtful declarer would want to make this claim. But the claim itself -- "heart to hand,....." -- has no doubtful points.

It is possible that the ruling would be just down 1, if you allowed that there was any doubt about what East would return. ("Gee, should I play a card to the good dummy, or should I try hearts?").

The World Bridge Federations Laws Commission has also commented on this, saying "Director must allow correction of the revoke [of course] and then determine the claim as equitably as possible, adjudicating any margin of doubt against the revoker."

If you leave out the phrase "as equitably as possible", this could be interpreted as saying the same thing as the English regulations. But with that phrase, I think they are saying that down four is not equitable.