Vampyr, on 2017-February-27, 18:38, said:
Dummy's knowledge is irrelevant. He must play dummy's highest card if there are other players yet to contribute to the trick. It does not matter if such a player has already shown out; dummy cannot participate in the play.
Well, when dummy is asked to ruff, dummy recalls the auction and selects his lowest trump. When dummy is asked to play small, he looks to see which suit is led and plays the lowest card of that suit. In this case he is specifically required to play the lowest card that is known to win the trick. So he has to participate in the play, or there is no play.
If dummy is fourth to play, it is easy. If dummy is third to play, he plays the lowest card that is known to win the trick if his LHO has already shown out or is known from the play not to have a card of the suit led, otherwise he plays his highest card. If dummy is second to play, he has again to play the highest card unless both his RHO AND his partner have shown out, or are known not to have a card of the suit led.
I am sure this is not what is intended by the Laws, and I stand by my proposed correction earlier:
46B1(b) If he directs dummy to ‘win’ the trick he is deemed to have called the lowest card of the suit led that will win the trick if dummy is last to play; otherwise dummy has to play the highest card of the suit led.
It is up to the lawmakers to decide what to do if dummy does not have a card of the suit led. I would suggest that he is then obliged to play the lowest trump that wins the trick if last to play, his highest trump but only if it higher than the highest trump played so far to a trick, if not last to play, and any card that declarer specifies without restriction if it is not possible for dummy to win the trick. Complicated but necessary!
I prefer to give the lawmakers credit for stating things for a reason - barmar