Chapter 8, Mishna 5, 6
Does an absent resident restrict his neighbors from carrying on Shabbos in a shared courtyard if he didn’t join in their eruv before leaving? Depends on whether he’s Jewish or not, and whether he’s definitely gone for all of Shabbos or not, and whose opinion you’re following: Rabbi Meir, Rabbi Yehuda, Rabbi Yosei, or Rabbi Shimon. The interesting case is when your Jewish neighbor goes to spend Shabbos with his grandkids: if at his daughter’s house we have a different outcome than if he goes to his daughter-in-law’s house! If a cistern lies under the boundary wall between two courtyards without a joint eruv, may we draw water from it on Shabbos?