Dedicated in memory of Lester Osband, Eliezer ben Avraham Nechemiah, Yardaena's grandfather a"h, whose yahrzheit is 2 Kislev. || A series of mishnayot checking the boundaries of what's allowed on Shabbat, ostensibly about carrying, but, it turns out, not only. To wit, a back door that is relatively makeshift, where opening the door fundamentally seems problematic in term of "building." Note how the Gemara elaborates beyond the mishnah here. Also: The story between R. Yehoshua and a heretic, and the puzzling, intriguing discussion of thorns, on literal and perhaps metaphorical levels. And - another mishnah: opening your door into a public domain, to enter or exit a private domain (or vice versa). R. Meir recommends a vestibule to convert public domain to karmelit, at least. The case specifically of poultry shops (or perhaps wool shops) in the Jerusalem marketplace. And the Gemara then notes just how unusual the Jerusalem marketplace was, perhaps, from some other cities. (See the book of Nechemiah, if you get a chance)