Daf Yomi - Sukkah 21 - A bed without shade

The Mishna states that one who sleeps under a bed inside a Sukkah does not fulfill his obligation. The Gemara explains that this is referring to a bed which is higher than ten tefachim, which creates a barrier between the person and the Sukkah. The Rishonim question this, as we find elsewhere that something which is even a tefach high is considered an ohel. Why, then, is there a concern only regarding a bed that is ten tefachim high? The Rif writes that the reason one does not fulfill his obligation of dwelling in a Sukkah is because the bed is ten tefachim, and this would constitute a Sukkah within a Sukkah and for this reason one does not fulfill his obligation. There are various challenges to the explanation of the Rif. The Baal HaMaor disagrees with the Rif. The Ramban in Milchamos offers a novel approach that explains why one who sleeps under a bed inside the Sukkah does not fulfill his obligation. The Ramban writes that the s’chach on top of the Sukkah is deemed to be invalid with regard to the space under the bed. The reason for this is because the s’chach cannot provide shade under the bed as the bed is providing shade. One would assume that the Sukkah should be valid, but one cannot fulfill his obligation. Thus, according to the Ramban, the Sukkah is invalid with regard to the one sleeping under the bed, because the Sukkah is not providing the person with shade.