Dear Rav Kornfeld,
The gemara explains that the din of "Ro-in" applies only if the top korah is within 20 amos or the bottom korah is above 10 tfachim. But the meforshin explain (Suka 22b) that the distance between the two korahs must be less than three tfachim since we still need to connect them through the din of "Levud'. Yet, the gemara states that if you don't use the din of "Ro-in" then we cannot connect the two korahs.
Question: Why not ? Can't the din of "Lovud" connect the two korahs, without using the din of "Ro-in" ? Unless, the case we are referring to is the very narrow case whereby the lower korah is diagonally further than 3 tfachim away from the top korah, and therefore lovud can only apply if by raising through "Ro-in" straight vertically the lower korah and bring it next to the top korah the distance bewtween them will be less than three tfachim, and also if if by moving through "Ro-in" straight horizontally the lower korah and bring it right below the top korak, the distance betwen them would again be less than three tfachim. My conclusion is that only in such very narrow case we would need the din of "Ro-in" besides the din of "Lovud" to allow two narrow unleveled korahs to be usable.
Is that really correct ?
Thank you in advance for you response.
Your talmid, Nosson Munk.
In the Chidushim of Rabeinu Chaim ha'Levi (Hilchos Sukah, end of 5:21), Reb Chaim asks a question very similar to yours. He answers that Lavud only makes two sections of a Korah be considered attached to each other, but it cannot serve to lower the upper Korah so that it be considered resting on top of the Mavoy . Rather, the Korah remains higher than the Mavoy. To lower the Korah to the Mavoy, it is necessary to utilize the principle of "Chavut Rami" (that is, what our Sugya calls "Ro'in"), which makes the Korah be considered as if it was lowered and is now resting on top of the Mavoy.
It should be noted that Reb Chaim there mentions that the Rishonim dispute this theory. Nonetheless, in our case your question does not pose a difficulty even without Rav Chaim's point. We find in the Gemara in Sukah there that the Amora'im argue whether we say "Chavut Rami" ("Ro'in") or not. It is according to Abaye, who maintains that we never say "Chavot" at all, that we do not join the Koros together unless they are within three Tefachim of each other, and indeed his reason is because of Lavud! (Abaye is explaining the opinion of Rebbi Yosi bar'Rebbi Yehudah in the Beraisa in our Sugya. The Tana Kama of the Beraisa here does not even hold of Lavud in such a situation regarding Korah, because of the reasoning that Tosfos explains here -- we require a Korah that is fit to hold up a brick without any Halachah l'Moshe mi'Sinais.)