Responsa על בבא בתרא 71:22

Q. B bought property from a Gentile which bordered on A's property. Before paying for it, B, to acquire possession, did some digging in the Gentile's yard in the presence of witnesses. After B did so, but before he had paid the money to the Gentile, A constructed apertures for windows in his wall facing the property. Did A acquire rights to window lights?
A. In city property digging is not considered a valid act of possession. Likewise A did not acquire any rights to window lights since a Gentile does not renounce his rights to his property before he receives the money, and the Gentile's property was, therefore, not (res nullis) ownerless. However, before paying money to the Gentile, let B perform a valid act of possession (such as locking a door, fixing or breaking part of the fence, etc.); otherwise A will acquire rights to window lights during the interval between the paying of the money and B's taking formal possession, since during such interval the Gentile's property will be res nullis.
SOURCES: Cr. 63–64; Pr. 28–29; L. 338; Mord. ibid.

Q. A had lived undisturbed for more than three years in T when the community ordered him to leave the place because he had received no permission from it to establish a residence there. A claims that the settlement ban against new settlers had been waived for his benefit by all the members of the community who lived in T at the time. The latter deny A's claim.
A. The removal of the ban against settlement by waiver is accepted by the communities as legally binding, although, in talmudic law, rights in real property cannot be waived or relinquished unless the waiver be accompanied by a formal act of possession. But since the community denies A's claim, A must produce proof that the ban against settlement had been waived in his favor. A community is in complete possession of its rights and does not have to protest any encroachments on such rights. Therefore one can not claim usucapion as a factor in obtaining possession of community rights. This law is accepted throughout this Kingdom.
SOURCES: Pr. 46; L. 351; Mordecai Hagadol, p. 308a.

R. Asher disagrees with R. Hayyim Eliezer, and maintains that the rule of Asmakta is not applicable in this case. B is considered the agent of A, since the latter voiced no protest when B bound himself, in the presence of A to reconcile C for damages, in the event of a breach of promise. Under these arrangements, the sale was then completed, and the fulfillment of the terms rested with A.

Q. A had lived undisturbed for more than three years in T when the community ordered him to leave the place because he had received no permission from it to establish a residence there. A claims that the settlement ban against new settlers had been waived for his benefit by all the members of the community who lived in T at the time. The latter deny A's claim.
A. The removal of the ban against settlement by waiver is accepted by the communities as legally binding, although, in talmudic law, rights in real property cannot be waived or relinquished unless the waiver be accompanied by a formal act of possession. But since the community denies A's claim, A must produce proof that the ban against settlement had been waived in his favor. A community is in complete possession of its rights and does not have to protest any encroachments on such rights. Therefore one can not claim usucapion as a factor in obtaining possession of community rights. This law is accepted throughout this Kingdom.
SOURCES: Pr. 46; L. 351; Mordecai Hagadol, p. 308a.

Q. A went to a distant country, leaving behind a wife and a daughter. His wife betrothed her daughter to C and promised him a dowry. C demanded that A's brother, B, become surety for the dowry. B did so, and A's wife deposited valuables with B to be used in the discharge of B's suretyship. A's wife died. When A returned, he demanded that B restore to him the valuables his late wife had entrusted to B.
A. A's wife had no right to promise a dowry or give anything to B or C without A's permission. Her promises and gifts were, therefore, void and B must return to A the valuables A's wife had deposited with him.
SOURCES: Pr. 858.