Responsa על גיטין 74:15

Q. A claims that he lent two pounds to B for investment purposes for one year, on condition that B pay him one pound if B's profit from this investment should exceed one pound, or the whole profit in case B's profit be less than one pound. B, however, claims that he was to pay A a uniform interest at the rate of one pound a year, and that it was a usurious transaction, and, therefore, not binding.
A. A's claim is sustained. Since A could have received a pound a year legally, had he lent the money to B through a Gentile, we must believe the truth of his (A's) present claim.
SOURCES: Cr. 57; Pr. 146; Rashba I, 871.

Q. A claims that L(eah) delivered him into the hands of Gentiles and caused him a loss of one hundred and five pounds. L denies A's charge. A further claims that he lent L twelve pounds for investment purposes to share equally in the profits. L avers that A lent her ten pounds upon interest [the interest was to be two pounds], that she has repaid five pounds and still owes him five pounds of old coins.
A. Regarding the first charge, if L will take an oath in support of her claim, she will be free from obligation. Regarding the latter claim, although I have heard in the name of R. Tam that the principle "a person will not let stand what is permitted and eat what is forbidden", as applied to the case where the creditor claims to have lost his prosbol (Git. 37b), is also applicable to a case such as the one mentioned above, some great scholars draw a clear distinction between the case of prosbol, where the debtor does not know whether or not the creditor has had a prosbol, and a claim such as the one mentioned above where the debtor knows the terms of the agreement, and his denial, therefore, of the creditor's claim, ought to carry weight. Moreover, R. Tam's decision probably applies only when the creditor had received a pledge and, thus, was in possession of his money. But, in our case, A seeks to collect. Therefore, L may take an oath to the effect that she owes A only five pounds of old coins, and, after repaying that sum, be free from further obligation.
SOURCES: Cr. 167; Am II, 143.

Q. A claims that he lent two pounds to B for investment purposes for one year, on condition that B pay him one pound if B's profit from this investment should exceed one pound, or the whole profit in case B's profit be less than one pound. B, however, claims that he was to pay A a uniform interest at the rate of one pound a year, and that it was a usurious transaction, and, therefore, not binding.
A. A's claim is sustained. Since A could have received a pound a year legally, had he lent the money to B through a Gentile, we must believe the truth of his (A's) present claim.
SOURCES: Cr. 57; Pr. 146; Rashba I, 871.

Q. At the time the tax was collected B did not pay any tax on an apparently bad debt. Shortly thereafter, A helped B to settle with the debtor for part payment of this debt. A, then, said to B that he would not be expected to pay taxes on the original value of the debt. Subsequently some members of the community summoned B to court regarding the tax on the debt, and the court reached a certain decision. A, however, was not satisfied and, as a member of the community, summoned B to court again. The latter claims that A's statement mentioned above proves that A had no case against him. A, on the other hand, contends that B swore to pay a tax on the value of the debt at the time the tax was collected. B denies this claim, while A has no disinterested witnesses to support his contention.
A. If A was in town when B was first summoned to court, he should have appeared in court at that time to press his claims. Even if A was out of town at the time, if B has complied with the court's decision in the matter, he is under no obligation to A. B is not required to take an oath denying A's claim, since no oath is imposed for the purpose of forcing compliance with an alleged former oath. On the other hand, A's statement to B did not, in itself, absolve B from obligation to A, since a person, sometimes, does not reveal his real arguments and claims to his opponent until they both appear at court.
SOURCES: Cr. 167; Am II, 136.

Q. A lent money to B on condition that they share equally in the profits. After a Sabbatical year passed, B refused to pay his debt to A, claiming that the Sabbatical year released him from the obligation. A is ignorant of the fact that were he to claim that he had a prosbol, which was lost, he could collect his debt in full. May the judge inform A of his rights?
A. No, he may not. In talmudic times, people often wrote prosbols; therefore, a judge was allowed to inform a creditor of his right to claim that he had had a prosbol but lost it. Nowadays, however, people rarely write prosbols and a judge is not permitted to suggest to a creditor to put forth an unusual claim.
SOURCES: Pr. 972; L. 198; Rashba I, 1075; Tesh. Maim. to Mishpatim, 10; Mordecai Hagadol, p. 219d; ibid. 369a.