(Mishnah): If one supported his Sukah with the frame of a bed, it is valid.

R. Yehuda says - If the Schach cannot stand by itself, it is invalid.

(Gemara - R. Imi): The reason that R. Yehuda disqualifies it is because there is not ten Tefachim from the inside (the mattress) of the bed until the Schach. (But according to the Chachamim, we view the bed as if it is in the Sukah and the height of the Sukah is measured from the actual ground, which means that the height is ten Tefachim.)

Reason #2 (R. Ba): The reasoning of R. Yehuda is that one may not support his Sukah with something that contracts Tumah.

Question: The Beraisa teaches that there was a story of the people of Yerushalayim who would stand up their beds in front of their windows and put Schach on top. If you say that R. Yehuda disqualifies because one may not support his Sukah with something that contracts Tumah, how could the people do this?

Rather, the reasoning of R. Yehuda is like R. Imi earlier (c).