He played diamonds, and South discarded a heart on the third round.

Only then will South know whether to discard a heart or a club on the diamond winner.

He led the club queen, and South discarded a heart.

He then led a club and discarded a heart from the dummy.

West thought for some time, then discarded a heart.

But West discarded a heart and there was still work to do.

He then led the club jack, discarding a heart when East played low.

If East had played low, declarer was going to discard a heart.

West therefore discarded a heart, but that was no better.

East discarded a heart, and West won with the 10.