Responsa sobre Eruvin 7:12

If the occupants of court-yards which open into a common alley-way, have associated their court-yards through the ceremony of shittuf (cf. M. Erub. 7, 6), the courtyards, together with the alley-way, become a single domain within which objects may be carried on the Sabbath. Such a ceremony renders unnecessary any further association of the different premises within each court-yard through the ceremony of Erub.
SOURCES: Pr. 89; cf. Hag. Maim., Erubin 1, 9.