B should pass both the queen and the knave. By passing the second trick, if the dealer fails to overtake, or if the dealer does not hold two re-entry cards, the suit cannot be made.
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Y has an entry card. B should refuse to win the trick, trusting that Z has no other card to lead.
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A should refuse to cover the honour. If he waits until the third round, the suit is blocked. Z may have no re-entry card.
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In this case, the honour should be covered. If Z holds the ace, the suit is blocked.
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A should cover the ten led. It may establish the king and nine in B’s hands. If Y has no card of re-entry B can then hold up.
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