At Trick 4, A having already shown his suit does not discard from it, as there is still a possibility of bringing it in (see pp. [104]-6), and his king of clubs is sufficiently protected even after the discard.
If Z parts with the last trump at Trick 6, and leads diamonds, A, on the second round of diamonds, will unguard his king of clubs, knowing his partner to have a heart to lead him (see fall of the heart suit, Tricks 1, 4, and 5), will bring in all the hearts, and win the odd trick.
HAND XXX.
See Refusing to win the second round of a suit, pp. [143], [144].
B's Hand.
- A♠, Qn♠, Knv♠
- 8♥, 4♥
- A♣, 7♣, 2♣
- A♦, Qn♦, Knv♦, 5♦, 2♦
Score: Love-all.