Responsa על בבא בתרא 271:10

Q. A demands from B the money his mother deposited with B, to be given to A after her death. B claims that A's mother gave him the money on condition that he return it to her, in case she needs it herself, or else give it to A after her death.
A. According to B's statement, A never gained title to the money since it was not given to him as a gift causa mortis, and he did not perform the formal act of possession necessary in order to gain title to an ordinary gift. His brothers, therefore inherited their share of the money. However, if A claims that he was present when his mother deposited the money with B, and that this money was thus deposited specifically for his benefit, as a gift causa mortis, B must swear that the facts are as he claims them to be.
This Responsum is addressed to R. Menahem ha-Levi.
SOURCES: Cr. 38; Pr. 420–421; Mord. B. B. 592; Mordecai Hagadol, p. 321c.

Q. B promised his young daughter in marriage to A's minor son. He gave A a written document obligating himself, from the time of the promise, to be A's debtor for 20^*In some sources (Pr. 50, L. 355) the reading is “marks.” The discrepancy arose because of the similarity of the two Hebrew letters of Khaf and Beth, which stand for 20 and 2 respectively. The Cremona source and the Mord., however, used the word Esrim, 20, specifically. marks should his daughter refuse to accept kiddushin from B's son when he will have arrived at his majority, or in case A himself should refuse to accept the kiddushin for his daughter. B died before A's son reached the age of 13, and his daughter married someone else. Now A demands the 20^*In some sources (Pr. 50, L. 355) the reading is “marks.” The discrepancy arose because of the similarity of the two Hebrew letters of Khaf and Beth, which stand for 20 and 2 respectively. The Cremona source and the Mord., however, used the word Esrim, 20, specifically. marks from B's heirs.
A. Since B has been prevented, by death, from fulfilling his promise, he never became obligated to pay the 20^*In some sources (Pr. 50, L. 355) the reading is “marks.” The discrepancy arose because of the similarity of the two Hebrew letters of Khaf and Beth, which stand for 20 and 2 respectively. The Cremona source and the Mord., however, used the word Esrim, 20, specifically. marks to A. Consequently his heirs owe nothing to A.
This question was also sent to R. Meir by his father, R. Baruch, who was one of the judges in this case.
SOURCES: Cr. 31; Pr. 50; Pr. 939; L. 355; Mord. B.M. 247; cf. Jacob Weil, Responsa 105; ibid. 142.