The case of 2 homes that separated by 3 ruins. Each can dump things into the ruin closest to them, respectively, but they are prohibited from using the middle one. (Though halakhah says they can both use the middle). R. Elazar hears this and goes to confront Rav (as we last saw him go confront Shmuel - never mind that Rav and Shmuel lived in different places!). But didn't Rav himself say that the up-people and the down-people run into trouble. But Rav has a quick retort - that the configuration of these homes and ruins are more complicated than R. Elazar was assuming. Also - The case of eruv chatzerot for a gatehouse - it's not quite a house, it's a passageway. But if someone lives there, can that person use the eruv? Host the eruv? What about making an eruv chatzerot from the food that's part of a Friday meal? What do you need for a shituf mavoi. And we circle back through the cases and issues.