QUESTION: Abaye and Rava argue about the status of an Achsadrah on which Sechach was placed. RASHI (93a) explains that the Achsadrah has two walls. In order to be a valid Sukah, there must be at least three walls. Abaye says that we apply the principle of Pi Tikrah Yored v'Sosem, and thus the structure is a valid Sukah. Rava says that we do not apply the principle of Pi Tikrah in this case. The Gemara suggests that the argument between Abaye and Rava is the same as the argument between Rav and Shmuel, who argue about the application of the principle of Pi Tikrah.

How can the Gemara suggest that the argument between Abaye and Rava is comparable to the argument between Rav and Shmuel? In the case in which Abaye and Rava argue, the structure has two walls, and, according to Rashi, Shmuel agrees with Rav that Pi Tikrah works as long as there is one wall!

ANSWER: The RITVA explains as follows. The Gemara eventually concludes that it is unlikely that Pi Tikrah should be able to work in the case of an Achsadrah with Sechach on top, because the boards on top of the Achsadrah were not made l'Shem Sukah, for the sake of serving as a Sukah. Even though the Sukah does not have to be made Lishmah, in order for Pi Tikrah to apply the boards must be placed there l'Shem Sukah.

The Ritva suggests that the Gemara knew all along that Pi Tikrah does not apply when the boards were not placed there l'Shem Sukah. Therefore, even if there are already two Mechitzos, Shmuel -- who says that Pi Tikrah does not work when there are no Mechitzos -- maintains that Pi Tikrah does not work in this case. However, the Gemara assumed that Rav -- who applies the rule of Pi Tikrah even when there are no Mechitzos -- would apply Pi Tikrah even when the Mechitzos were not made l'Shem Sukah at all.