it seems to me that the gemorahs question "is it permitted to use the postshards of wine to support a bed" is a question of whether it is permitted since you have absolutely no need for the nesech wine and you are not benefitting from it at all---i dont see what that has to do with rotzeh b"kiyumo---r.b. means that you want the nesech wine -but in our case i dont want the nesech wine at all
SHMUEL GOTTESMAN, brooklyn, ny u.s.a.
The case of the Gemara is where the Yisrael wants the shard containing the wine not for the wine but for the shard. That is what the Gemara calls 'Rotzeh be'Kiyumo through something else'. On the one hand he wants the wine to remain inasmuch as it is an intrinsic part of the shard, whereas on the other hand, it is the shard he wants and not the wine.
Do you still have further questions?
Be'Virchas Kol Tuv,
Eliezer Chrysler