Daf Yomi - Sukkah 18 - Highlights

A sukkah that is eight amos precisely and one alternates between beams four tefachim wide and valid s'chach four tefachim wide, the sukkah is valid even according to the opinion that holds beams four tefachim wide disqualify a sukkah. The reasoning is because the sukkah will have eight contiguous tefachim of valid s'chach and with the principle of dofan akumah, the sukkah will be valid.

Abaye maintains that if one has an open area of more than three tefachim in a large sukkah, the sukkah will be valid if he reduces the open area by placing valid or even invalid s'chach in that area. If it is a small sukkah, it must be reduced through eligible s'chach.

The Gemora cites a debate regarding a sukkah that has less than three tefachim of open area in the middle of the sukkah. One opinion holds that the principle of lavud can only be applied on the side of the sukkah but not in the middle. Proofs to both opinions from halachos regarding eruvin and tumah are cited and refuted.

A tzachanta fish originating from the Bav river was ruled to be kosher because the mud there doesn't support the growth of the unkosher fish. However, they subsequently ruled that these fish are prohibited because there are other rivers that now flow into the Bav River.

If a person placed s'chach on a porch that has pillars in front of it, the sukkah is valid. This is referring to a porch where the roof is more than four amos away from the house wall and thus the principle of dofan akumah would not apply. The pillars are deemed to be walls because they are spaced less than three tefachim away from each other and with the principle of lavud, the gaps are regarded as closed.

If however, there are no pillars in front of it, there is a debate between Abaye and Rava. Abaye maintains that the sukkah is valid because we apply the principle of "the tip of the roof extends down and we close." Rava disagrees with this and holds that the sukkah is not valid.

The Gemora cites an argument between Rav and Shmuel regarding a pavilion in a valley and deliberates if it is analagous to the debate between Abaye and Rava. Rav maintains that one is allowed to carry on Shabbos inside the pavilion because we apply the principle of "the tip of the roof extends down and we close." Shmuel disagrees and rules that one is only permitted to carry within his four amos. The Gemora concludes that they are not parallel because Rav would hold of this principle only by the pavilion where the walls were made for it, however by the porch, the walls descending from the roof were intended for the porch and not for the sukkah.