Responsa for Bava Batra 71:1
לדידי אמר לי עכו"ם דמינך זבנה מהימן מי איכא מידי דאילו עכו"ם אמר לא מהימן ואילו אמר ישראל משמיה דעכו"ם מהימן
'The non-Jew said to me that he had bought it from you,' his plea is accepted. [But] can it be possible that a plea which would not be accepted if put forward by a non-Jew<span class="x" onmousemove="('comment',' Because, as stated above, the non-Jew can only prove his right by producing the deed of sale. ');"><sup>1</sup></span> should be accepted if put forward by a Jew in the name of a non-Jew? Raba therefore corrected himself as follows: If the Jew pleads, 'The non-Jew bought it from you in my presence and sold it to me,' his plea is accepted, because if he had liked he could have brought against him [without fear of contradiction the still stronger plea], 'I myself bought it from you.'
Teshuvot Maharam
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.
Teshuvot Maharam
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.
Maharach Or Zarua Responsa
Teshuvot Maharam
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.
Teshuvot Maharam
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.