Responsa for Bava Batra 306:1
אמר רבה הרי מת והרי קברו מוכיח עליו אמר ליה אביי השתא ומה ספינה שרובן לאבד נותנין עליהן חומרי חיים וחומרי מתים חולין שרוב חולין לחיים לא כל שכן
Rabbah said: Behold, he is dead and his grave indeed proves this.<span class="x" onmousemove="('comment',' Lit., 'upon him'. Since there is no evidence that the testator recovered from the illness during which be made the gift, the fact that be is dead is sufficient ground for the assumption that be died from that illness. ');"><sup>1</sup></span> Abaye [however] said to him: [How] now! If [in the case of] a ship [that sank], where most of the passengers<span class="x" onmousemove="('comment',' Lit., 'most of whom'. ');"><sup>2</sup></span> are doomed to perish, [we] apply to the victims<span class="x" onmousemove="('comment',' Lit., 'upon them'. ');"><sup>3</sup></span> the restrictions of living<span class="x" onmousemove="('comment',' If among the victims there was, for example, an Israelite who had married the daughter of a priest, it is assumed that he remained alive, and his wife is, consequently. forbidden to eat of the heave-offering. Had it been assumed that her husband was dead she, as the daughter of a priest, would have regained her right to eat of the heave-offering (cf. Git. 28b). ');"><sup>4</sup></span>
Teshuvot Maharam
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.