West led the king of diamonds. East started an echo with the 9. The ace of diamonds was then cashed and West quite properly laid down the ace of clubs and then the jack of diamonds. The dummy played low and, since his partner's jack was high, East took a worthless discard. South, of course, ruffed, extracted trumps and claimed the balance of the tricks.
At the conclusion of the hand, there were mutual recriminations between East and West. East asserted that he did not wish to use his trump when his partner's diamond was high, because for all he knew declarer might have another diamond. This was unsound for two reasons. First of all, West must be presumed to hold five diamonds in view of his vulnerable overcall. Secondly, if declarer had another diamond, West would know it. That would render it completely pointless to cash the ace of clubs; West would have kept that card so that partner could re-enter his hand to lead the fourth round of diamonds.
East, of course, should have played his high trump on partner's good diamond (a technique known as the uppercut), forcing the king, and West would have cashed the setting trick with the jack of spades. West's play was quite thoughtful because he realized that the only hope to defeat the contract was to find East with the king or queen of spades. Cashing the ace of clubs should have put East on his guard. But perhaps West should have gone one step farther in his precautionary measures and led a small diamond instead of the jack. This would have made it compulsory for East to trump, and let us be charitable enough to assume that he would have trumped with the queen rather than with the 9.