An example of a "Dummy Reversal".
Bridge Column for March 28, 2003, Harvey Bernstein
Both Sides vulnerable.  North deals.
                              North
                              S: 4           
                              H: A K Q 4     
                              D: A J 8 6 5   
                              C: K 6 4   
            West                             East
            S: K 8 7 6 2                     S: Q 10 9 5 3 
            H: 2                             H: 8 7 6     
            D: Q 9 2                         D: K 10 4            
            C: J 9 5 3                       C: 8 7         
                              South                         
                              S: A J  
                              H: J 10 9 5 3 
                              D: 7 3       
                              C: A Q 10 2 
          The Bidding:  
                  North    East    South    West                  
                   1D      Pass     1H      Pass
                   3S      Pass     4C      Pass
                   4D      Pass     4S      Pass
                   4NT     Pass     5H      Pass
                   5NT     Pass     6C      Pass
                   6H      Pass     Pass    Pass
     Today's hand is from a duplicate game.  North's double jump
shift to three spades is known as a "splinter" bid.  It shows
good heart support, a singleton spade (or possibly a void), and a
big enough hand to demand game.  South cooperates by cue bidding
the ace of clubs.  North shows the ace of diamonds.  
     South goes past the heart game to cue bid the ace of spades.
North bids four no trump, asking for key cards.  Five hearts indicates
two key cards without the queen of hearts.  North bids five no
trump, confirming that all five key cards are accounted for and
asking for kings.  When South shows no kings, North stops at six
hearts.
     West opens the six of spades which comes around to the queen
and the ace.  How do you think that declarer should proceed
     Even looking at all four hands it is not easy to see that
this is a perfect hand for declarer to "reverse the dummy".  This
is a process where declarer works to make the dummy the hand that
will, in the end, have the tricks to assure the contract.
     Your analysis should determine that if clubs do not divide
three-three you may have a problem in that suit, and there is
always a diamond to lose.  Also, if diamonds divide no worse than
five-one, you should be able to make twelve tricks by trumping
diamond losers in hand.  To that end, you play a diamond to the
ace at trick two and then play a small diamond from both hands.
Whichever defender wins this trick will probably return a spade
because it is safer than a club.  
     Trump the spade lead low in dummy and lead a third diamond,
trumping high from hand.  Both defenders follow to this trick and
all that is left to do is finish drawing trumps and claim.  
     One of the clues to recognizing a hand where a dummy
reversal will provide the greatest number of tricks is when you
see that the trump spots in the dummy are big enough to capture
the outstanding trumps after the high trump in hand are used to
cover dummies losers.
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Bernstein is a free-lance writer in Solon.