Yosef Karo

“ Paragraph 3 - If there were three people who each enclosed an area forthemselves next to one another, and they made an eruv, if the outer ones are wide and the middle area is thin, such that the inner one is open completely [on each side] to the outer ones and the outer ones have partial walls on every side, they are allowed as much space as they need in the middle one even if it is very large, because it is as if they all live in it, and there are three of them. ”

“ What are the parameters of this discussion? When the openings between them are not more than ten [amot] . If they are [more than ten] , it is an opening in the walls and even the more enclosed ones are forbidden. ”