Q: I found a sefer in a street that mostly gentiles pass through. May I keep it?
A: Although we usually presume yei’ush when an item is lost where mostly gentiles pass, we do not presume yei’ush regarding seforim or others item distinctly for Jewish use, so that hashavas aveidah applies. This is because the owner knows that even if a gentile will find the item, he has no use for it and will sell it to a Jew, so that he hopes to be able to reclaim it (Rema 259:3; 235:8).
Similarly, if a gentile stole a sefer and sold it to a Jew, the buyer must return it to the owner, because we do not presume yei’sush, so that the buyer cannot fully acquire it. Nonetheless, the owner must reimburse whatever amount the person spent to buy the item from the gentile (Rema 25:8).
However, if the seforim were plundered in a war, such as in the Holocaust, we presume yei’ush, like other natural catastrophes that the owner has no control over (Pischei Choshen 3:4[8]).
