Question: Ulla and Rav Ashi argue over the status of a valley. Ulla says it is always a Carmelit , but the reason the Mishna calls it a Reshut Hayachid is because it is not a Reshut Harabim.
Could clarify for me the opinion of Rav Ashi.?.
Rav Ashi's intention is that indeed, an un-enclosed valley is a Karmelis. The Mishnah in Taharos that calls it a Reshus ha'Yachid is talking about a "Karpaf," which is a valley enclosed by Mechitzos, and therefore it is a Reshus ha'Yachid because of the Mechitzos.
If so, then what is the Mishnah teaching when it says that it is a "Reshus ha'Yachid with regard to Shabbos?" If it has Mechitzos, then why not! Rav Ashi answers that the Mishnah is saying that even though no one lives in the valley, and since it is a very large area the Rabanan forbid carrying more than four Amos within it (like in a Karmelis), nevertheless it is a Reshus ha'Yachid mid'Oraisa and one who carries from it into a Reshus ha'Rabim will be Chayav.
Is that what you were interested in? Be well,
-Mordecai