When you have an outer house and an inner house, is the outer house a gatehouse, which would have implications for eruvin - in some ways, a study on how different spaces function differently with regard to different people. Chapter 7: A wndow in the wall that separates two courtyards - at a specific point in the wall - does that interfere with the partition function? Are the two courtyards one, or davka two? For the first time (we think), we see the possibility of an option to join, simply because you want to. (Too small, and the window would be lavud - the kind of gap that is considered negligible.) Also - The case of a round window - of 24 tefachim. Measurements include squaring the circle. But the measurements seem to be inexact. And R. Yochanan is taken to task for it. Note also that round windows are not all the common - they're that much harder to make! Plus: A wall between two courtyards - you need two eruvin, one for each side. If there were fruit on top of the wall, and both sides can access the fruit, either side can climb up to eat up there. A breach in the wall, however, can nullify that requirement for two eruvin, depending on the measurements.