Nedarim 5:4-5

Nedarim 5:4 If a person said “I am cheirem (banned) to you,” the one to whom he spoke is prohibited. If he said, “You are cheirem to me,” the one who vowed is prohibited. If he said, “I am to you and you are to me,” they are both prohibited. Both are permitted to use things for the pilgrims who come from Babylonia and both are prohibited from using city property (in which they would both be considered partners).

Nedarim 5:5

The things for the pilgrims who come from Babylonia include the Temple mount and courtyards, and the wells in the middle of the roads. City property includes the town square, the bath house, the shul, the aron and the communal books. The problem of being prohibited from city property can be avoided by each party granting his share in the communal property to the community leader. Rabbi Yehuda says one may grant his share to the community leader or to a private citizen. The difference between granting one’s share to the community leader or to a private citizen is that one who grants his share to the community leader does not have to perform a formal act of transference. The Sages say that both a private citizen and the community leader require that a formal act of transference be performed. The reason they said to grant the share to the community leader was not because of any practical difference; they merely spoke of the community leader because granting him the share reflects the current practice. Rabbi Yehuda said that people who live in the Galilee do not have to transfer their shares to the community leader because this was already taken care of by their ancestors.