(Mishnah): A person who sleeps under a bed [in a Sukah] has not fulfilled his obligation.

R. Yehuda says - We used to sleep under beds in front of the Elders and they did not say anything to us.

R. Shimon says - There was a story of Tavi, the slave of Rabban Gamliel, who was sleeping under a bed.

Rabban Gamliel said to the Elders - Have you seen my slave Tavi who is a Torah Sage - he knows that slaves are exempt from Sukah, so he sleeps under the bed.

We learn from this that a person who sleeps under a bed does not fulfill his obligation.

(Gemara - Question): The Mishnah (earlier) teaches that 'he made spread a sheet as a two-poster bed'; but here you teach that one who sleeps under a bed, even though it is not ten Tefachim tall so it cannot be considered a tent, he has not fulfilled his obligation?!

Answer (R. Eliezer): There, the sheet is considered like his garment, as if he is sleeping in a Sukah with a garment draped over him; but here, even if the bed is not ten Tefachim tall, it is a separation between him and the Schach.

Question: The opinion of R. Yehuda seems to have switched - there (in Yerushalmi Pesachim 23b - Perek 3 Halachah 7) he said that action precedes study; but here he says that they would sleep under beds in front of the Elders. (Even though one does not fulfill his obligation this way, they were permitted to do so in order to learn from the Elders - this shows that study precedes action?!)

Answer: R. Yehuda held that one who sleeps under a bed is considered to be sleeping in the Sukah (in disagreement with the Tana Kama who holds that he may not do so, so at that time he was also performing an action).

Question: Certainly then, R. Yehuda has switched his opinion! In the Mishnah (earlier) R. Yehuda said that if there is no-one inhabiting the top Sukah, the Sukah underneath it is valid; this shows that if there is someone inhabiting the top Sukah, the lower one is invalid?! (Here also, there is someone sleeping on the bed above him, so how could R. Yehuda say that he fulfills his obligation?)

Answer (R. Yosa): There (a Sukah on a Sukah), there is an airspace above him; here there is not, as the bed is not ten Tefachim tall.

Question: The opinion of Rabban Gamliel seems to have switched - a Beraisa teaches that Tavi the slave of Rabban Gamliel would wear Tefilin and the Chachamim did not protest; but here, it appears that Tavi went under the bed out of fear that Rabban Gamliel would protest him sleeping in the Sukah...?

Answer: He only went under the bed in order to give more space to the Chachamim.

Question: If so, why did he not just leave the Sukah?

Answer: He wanted to hear the words of the Chachamim.