Can a yeshiva decide that any old sefarim which were left around its premises become hefker even if they did not put up a sign? They will put up a sign now (so any talmid who leaves sefarim around is agreeing to make his sefer hefker, but it could be that old talmidim will not see it. Perhaps there is an “umduna” that public institutions can do this after a certain amount of time (maybe thirty days), even if a sign is not put up? Or maybe there is still a chiyuv of hashovas aveida (on the hanhala and/or the other boys in yeshiva)? What is the halacha?
Answer from Horav Yosef Fleishman shlit”a.
I once asked Rav Eliashev zatsal and he said they can’t dispose of the seforim and Rav Moshe Feinstein also maintained that way. Therefore there is a mitzvah of hashavas aveido.