MB4 265a: Adjacent Cities and Techum (398:6-8)

Do Ruins of a building with only two walls and no roof extend the city limits?

Houseboats, shuls (with or without an attached dwelling) acting as an extension of a city for measuring the techum.

The techum of a bow-shaped city.

Two adjacent cities separated by at most 141 1/3 amot (70 2/3 amah for each city) are considered one city vis-a-vis techumin.

When do three adjacent cities combine to form one city for techumin?