Rabbi Aryeh Lebowitz

Nothing about shnei zesim, doesn't say anywhere in the Gemara.

They need shnei kezayis matzah.

How could it be that there's a halacha, they have to eat shnei zesim, and it doesn't say it anywhere in the Gemara, anything about shnei zesim.

So if Schechter in Sefer Eretz Hatzvi in Simen Dalin, Os Yud, points out that probably you could answer the Bir Halacha as follows.

The Shitas HaRambam, in the 7th paragraph of Al-Khazayin, is that there's a mitzvah, an independent mitzvah of Kheiros.

That every generation, a person has to be Laharos HaZatzmo, as if he's leaving Sheba and Mitzrayim, so when he has a meal, on the night of the Seder, he has to eat and drink Kishu Masev, Derech Kheiros.

Everyone has to drink Dalat Kosha, Shaliyayin, etc.,

And that's why the Ramah Paskin's in Tafayin Beisiv, Zayin, L'chadchila, you should lean for the entire meal.

So the Prisca Rav points out that Tosus and the Rosh disagree with the Rambam.

They hold that there is no mitzvah of cheiros.

It's that dalet kosos, the gerder of dalet kosos, is dalet brachos ala kos.

Haseba is the way to do the mitzvah of matzah.

The way to do the mitzvah of dalet kosos.

But it's not its own fulfillment of a mitzvah of cheiros.

It is a how-to within the mitzvah of salaylov.

So it turns out, according to the Rosh, the only time you have to do a Seba is when you're eating the Keziahs of Achilas Matzah.

Because that's the unique mitzvah salayla for the Lala Seder.

But not for the whole meal, like the Rambam says, an independent mitzvah of Kheiros.

Ah, so it makes sense, says Rav Shechter, that the sugya that's going to talk about the mitzvah of a Seba, according to the Rosh, is only going to talk about one Keziahs.

Because according to the Rush, the only Kezias that needs to actually be Beheseba is the Kezias that you're doing for Achilles Matzah.