Responsa על בבא בתרא 108:6

Q. B bought from a Gentile woman a house bordering on A's property. B agreed that the woman could remain in the house till the month of Heshvan (October). A and C claim that they were negotiating to buy the house before B appeared on the scene; that A has a partnership in the house since the beams of his house project into the wall of the Gentile's house; that the Gentile owed money to A; that B promised them not to buy the house; that the arbitrators reported to A and C, B's statement to the effect that A and C need not be concerned, and could rely on his word as a Jew that he would not buy the house; that the Gentile gave A and C the keys to her house, and that they opened it, measured the size and noted the arrangement of the rooms, the exits, and the entrances, and locked it, before B bought the house. They, therefore, demand that B transfer the house to them. B avers that he never promised A and C not to buy the house; and that he had negotiated to buy the house long before they did. The Gentile woman claims that A inserted his beams into her wall illegally.
A. A and C cannot force B to transfer the house to them, for the following reasons: a) B denies having promised A and C not to buy the house; b) if B did make such a promise to A and C, and then broke it he might be called Rasha (wicked) or Abaryana (renegade), but we can not force him to transfer the house to A and C; therefore, no useful purpose will be served by imposing an oath on B regarding such promise; c) although locking a house is considered a valid act of possession, and one may gain title to the property of a Gentile by taking possession thereof (Bechorot 13a), this rule applies only when such an act is accompanied by proper intention by both parties. However, before the two parties agree on the terms of the sale no such intention is possible; therefore, A's locking of the Gentile's house was of no consequence; d) the fact that the Gentile owed money to A does not vest in him the priority rights of an abutter, for, only a creditor who has a mortgage on a house, lives therein, and has a lease thereon so that he cannot be made to move before the year is up has the right of an abutter. Moreover, since A's property borders on that of the Gentile, B may assert: "I have driven away a lion from your neighborhood", and such assertion annuls the priority rights A could have claimed as an abutter, as a creditor, or as a partner; e) B's statement to the arbitrators constituted neither an oath nor a vow, but a mere assurance. Even if we agree with A, who has construed that statement to mean an oath, B may not be forced to transfer his house to A merely because he disregarded his oath. Thus A is not entitled to indemnity. Indeed, B should be fined for his sinful act (breaking his oath), but we do not have the authority to impose penalties. However, you, my teacher, and your community, if you find that a disgraceful breach of conduct was committed, you may impose a proper fine upon B, the money to go to charity. Finally, half of B's wall, upon which the ends of A's beams are resting, belongs to A; for, the presence of such beams is ample proof that the wall was held in partnership by the two neighbors.

Q. Complying with A's request, the ruler of town T gave A the authority to admit as settlers only those persons of whom A would approve. A claims that B asked him for permission to remain in T for one year telling him that he had settling rights in another place, thus admitting that he possessed no settling-rights in T. B claims that he does possess such rights in T, that his father lived there before him, and denies having asked B for permission to stay there. Should both, B and A, be permitted to stay in T, it might lead to grave consequences, even to the spilling of blood, since B's conduct is known to be corrupt. Rabbi Moses asked what course he should take with respect to their claims.
A. If A produces witnesses to the effect that B asked permission to remain in T for a year, B will have to leave the town, since by his asking for permission he admitted that he either possessed no settling rights there, or had foregone any rights he might have had. If A can produce no such witnesses, B has a right to dwell in T. However, because of B's wicked conduct, you, Rabbi Moses, should deprive B of his settling rights in T and require A to pay adequate compensation to B. I have often seen communities deprive one of their members of his settling-rights because of misconduct; your court that has the right to confiscate a person's money, surely has the right to deprive one of his settling-rights. You should force, therefore, A and B to leave the case completely in your hands to be decided either by arbitration or according to strictly legal requirements, and then you will be able to decide as you see fit.
R. Meir adds:
Your opinion that B lost his settling-rights because of the legal principle "the law of the land prevails" is untenable. The ruler of T gave A the authority to pass on new settlers, but he gave A no authority to dislodge old residents. Had the ruler of T granted A the authority even to dislodge old residents, the validity of such a grant would depend on the reasons that prompted the ruler to grant such authority. If A asked the ruler for such authority, then A has no right to exercise his authority since by his request he directly injured B's interests. But, if the ruler of T, on his own accord, said that he does not want any Jew to live in T unless he receive A's permission, then A may dislodge B because of the legal principle: "The law of the land prevails".
The decision of R. Isaac (b. Samuel, the Tosafist) in the case of the Jews who fled from their town and whose real estate the ruler of the town confiscated and, then, sold to other Jews, has nothing to do with our decision. In this latter case, R. Isaac rightly decided that the purchasers must return the property to the original owners (as compensation, the purchasers were entitled to the amount the original owners would have spent to regain their property) for the ruler had no right to confiscate real property that belonged to the Jews for generations. Such an act on the part of the ruler is not considered "law of the land" but is rather outright robbery, and, therefore, illegal. In our case, however, the ruler of T is the owner of T and has a right to admit anyone into his town, and to keep out of it anybody he wants to keep out. We cannot claim for B's benefit that his father bought permanent settling rights from the ruler of T and stipulated that he or his descendants could never be dislodged from T, for such transactions were very rare, even though such a stipulation if made would be binding and would render the act of the ruler dislodging B an illegal act.
The decision arrived at in the Talmud (B.B. 54b) accepting as binding the Persian law that if the owner of a field defaults in the taxes for that field, anyone who pays the taxes becomes owner of the field, also, has nothing to do with our case; for taxes on real property accumulate even when the owners are away, while Jews are not required to pay taxes to their overlord, unless they actually live in the domain of these overlords. For Jews are not subjugated to their overlords as the Gentiles are, in the sense that they have to pay taxes to a particular overlord even when they do not live in his domain. The status of the Jew, in this land, is that of a free land owner who lost his land but did not lose his personal liberty. This definition of the status of the Jews is followed by the government in its customary relations with the Jews.
SOURCES: Cr. 6; Pr. 101, 1001; L. 313; Mord. B. B. 559; Mordecai Hagadol, p. 253b. Cf. Agudah, B. K. 144; ibid. B. B. 74; Maharil, Responsa 62; ibid. 77; Terumat Hadeshen 351.