16 Poker Problem

The first condition, P doesn't know this card. Explain that the number of points in this card has two or more suits. If there is only one suit, then P should know, so the points with only one suit are excluded, leaving A, 4, 5 and Q.

The second condition, Q says P is unknown. Q knows the suit, so it is judged that P doesn't know, that is to say, all cards of this suit have more than one suit, that is, they can't contain cards other than A, 4, 5 and Q. If they contain cards other than these four points, Q can't be judged as P doesn't know. Just like if Q knew it was spades, maybe it was spades 3, Q wouldn't dare to say that P didn't know. So exclude the flowers and spades and leave the hearts or diamonds.

The third condition, P, is unknown. Because there are only hearts and diamonds left at this time, if the card point is one of 4, 5 and Q, then P should know, but P just doesn't know, so it can only be A.

The fourth condition, q knows. With the point number A derived above, plus the color that Q already knows, then Q will know.

Finally, a heart or a diamond. As for how Mr. S knows, there is really no solution.

PS: another version is: the third condition, p means known (inferred not a). The fourth condition, Q also knows (it is inferred that it is a square, but if it is a heart, Q does not know), and Mr. S finally concludes that it is a square 5.