Responsa for Ketubot 173:18

Q. B engaged A as tutor to his son. B said to A that since he, B, was unlearned and did not know whether or not A had sufficient knowledge to tutor his son, A must go to his (B's) relative C to be examined before entering upon his duties. A came to B's house and began to tutor B's son. Subsequently B discovered that A had never been examined by C. He, therefore, summoned A to court. A now declares himself ready to be examined, but B argues that A's present knowledge is no proof of his previous fitness for his position. Moreover, one witness testifies that at the time A undertook to teach B's son, he was not qualified to do so because of insufficient knowledge.
A. If A has now sufficient knowledge to teach B's son, the burden of proof lies on B that A did not have such knowledge at the time he was engaged. However, since B has one witness to support his claim, A must take an oath to the effect that he had sufficient knowledge at the time of the agreement. If A takes such oath, he will be entitled to collect his full wages from B.
SOURCES: Cr. 3; Pr. 488; Mord. B. B. 621. Cf. Agudah B. M. 172.

Q. B constructed a stone duct near A's wooden house. A objected and B made a written promise to compensate him for any damage the duct might cause to his house. A now demands that B remove his duct because it occasionally permits water and sewage to flow into his house, and he objects to being forced to sue for damages every time it occurs. B claims that water flows into A's house only when the duct breaks. He promises to keep the duct in good condition, but refuses to remove it.
A. B must remove his duct from A's wall for a distance of 3 tefahim (hand-breadths). If the water should, nevertheless, continue to flow into A's house, it is for A to protect his wall by whatever means he sees fit, but he can demand nothing of B.
SOURCES: Cr. 3, 4; Pr. 92; L. 357; Mord. B. B. 520.

Q. A and his wife drew up a document for the benefit of her son (A's stepson), in which was written: "Give to our son…" Does the expression "our son" invalidate the document since the beneficiary is not A's son?
A. A person who brings up an orphan in his house is in the same position as the orphan's father. Therefore, the phrase "our son" is quite appropriate. Moreover, the phrase in the document "to our mother so and so the daughter of so and so"… referring to A's mother-in-law, does not invalidate that part of the document as long as the name of the mother-in-law is given. For the term "son" or "mother" is an affectionate expression correctly used in this sense even when such relationship does not exist.
SOURCES: L. 242; Tesh. Maim. to Mishpatim 48. Cf. Maharil, Responsa 81.

Q. R. Moses, the plaintiff, was not present when the defendants, the Jewish inhabitants of Quedlinburg, took an oath in order to nullify the testimony of R. Moses' single supporting witness; must they take the oath again in the presence of R. Moses?
A. If the oath has been legally administered by a proper person (who is related neither to R. Moses nor to the inhabitants of Quedlinburg) there is no need for another oath.
This Responsum is addressed to R. Shemariah, and is the second communication regarding this case.
SOURCES: Pr. 231; L. 382; Tesh. Maim. to Haflaah, 1. Cf. P. 514; Mord. Ket. 296–7.