In this example, hearts are trumps and South's 2 is the last one remaining, and the lead is with North (dummy). Then North-South can take all tricks if East holds the ace of spades. A spade is led from the North hand; if East plays low, a diamond is discarded and the lead is repeated. If East never covers, North-South get three spade tricks and a trump. If East plays the ace, South trumps and leads a club to return to the dummy, which is high, so taking two spades, a trump, and a club trick.
