1) HALACHAH: CARRYING IN A MAVOY DIRECTLY OPPOSITE THE LECHI
OPINIONS: Abaye rules that one is prohibited from carrying in a Mavoy in the area at the entrance to the Mavoy that is adjacent to the Lechi ("Bein Lechayayim"). Rava argues and maintains that one is permitted to carry in a Mavoy in the area adjacent to the Lechi. Rava cites proof for his opinion from the ruling of Rebbi Yochanan that an area that is less than four by four Tefachim (a Makom Petur) is not a significant area in itself and is subordinate to the area in which it is found.
It is obvious that an area that is larger than four by four Tefachim is not a Makom Petur and one may not transfer an object from another Reshus into such an area. How would Rava rule in a case in which the area parallel to the Lechi is more than four Tefachim long (that is, the Lechi itself is more than four Tefachim long)? Would he rule that the area adjacent to the Lechi is considered a significant area in itself into which one is prohibited from carrying?
(a) TOSFOS (8b, DH ha'Kol), the RITVA, and other Rishonim explain that in such a case Rava would agree that one is prohibited from carrying in the area adjacent to the Lechi.
(b) The RIF rules like Rava and says that one is permitted to carry in the area adjacent to the Lechi. He does not differentiate between areas less than four Tefachim and more than four Tefachim, which implies that he maintains that Rava permits one to carry even if the area opposite the Lechi is four Tefachim or more.
The RAMBAN (in Milchamos) explains that although Rava cites as proof a discussion regarding a Lechi that is less than four by four Tefachim, he uses that discussion only to convince Abaye to agree with him at least with regard to an area less than four Tefachim. Rava himself, however, maintains that one is permitted to carry at the entrance to the Mavoy in the area adjacent to the Lechi even if it is larger than four Tefachim. He permits one to carry there not because that area is not considered a significant area in itself, but rather because he maintains that when the Lechi serves as a Mechitzah or as a Heker, its outer edge serves as the Mechitzah or Heker, and thus one may carry until the outer edge of the Lechi.
The Rif infers this from the fact that the Gemara questions Rava's ruling from the case of a Mavoy which was lined (she'Retzafo) with more than one Lechi. In that case, Raban Shimon ben Gamliel prohibits one from carrying past the inner side of the innermost Lechi (since all of the Lechis join to form one long Lechi through the principle of Lavud). The Rabanan prohibit one from carrying past the inner side of the outermost Lechi (since the Lechis do not join). Why does Rava not answer that in that case, the Lechis are longer than four Tefachim, and that is why one may not carry in the area adjacent to them? It must be that Rava maintains that one is permitted to carry in the area adjacent to the Lechi even when that area is more than four by four Tefachim. (See TOSFOS DH l'Raban Shimon ben Gamliel, who discusses this question.)
HALACHAH: The SHULCHAN ARUCH (OC 365:4) rules like the Rif and permits one to carry in the area adjacent to the Lechi even when the Lechi is more than four Tefachim long, provided that the Mavoy opens into a Reshus ha'Rabim and not into a Karmelis, as the Gemara says.
The MISHNAH BERURAH (365:25) points out, however, that the permissibility to carry in the area adjacent to the Lechi when it is more than four Tefachim is actually a Machlokes Rishonim, since Tosfos argues with the Rif regarding the status of such an area.
(A third opinion is that of the BA'AL HA'ME'OR, who rules like Abaye and prohibits one from carrying in the area adjacent to the Lechi in either case. He reasons that Abaye's ruling in this matter is based on his ruling with regard to "Lechi ha'Omed me'Elav" (see Eruvin 15a and Insights there), and that case is one of the few cases in which the Halachah follows the opinion of Abaye when he argues with Rava.)