All the roofs of a town are one domain, provided that one roof is not ten [fists] higher or lower [than the others] — [these are] the words of R’ Meir. But the Sages say: Each is a domain for itself. R’ Shimon says: Roofs, courtyards, and karpeifos are all one domain with respect to utensils which began the Sabbath in them, but not with respect to utensils which began the Sabbath in the house.