MB4 260a: Making an Eruv for an Entire City - part 3 (392:5-8)

If a city is a full-fledged רשות הרבים it has to be fully enclosed with walls and doors that are closed at night in order for carrying to be permitted. If not, an eruv chatzerot via tzurat hapetach is sufficient.

Separating a fully-enclosed city into separate shituf mavuot.

Dividing a mavui into two shitufin.

A city with a population of less than five doesn't need a minimal shiur of food.

Making a shituf mavuot on behalf of the entire city can be done without getting consent from all the Jews in the city based on זכין לאדם שלא בפניו.

If someone forgot to participate in an eruv.