Reference for Bava Metzia 43:5

ת"ש כיצד אמרו התורם שלא מדעת תרומתו תרומה הרי שירד לתוך שדה חבירו וליקט ותרם שלא ברשות אם חושש משום גזל אין תרומתו תרומה ואם לאו תרומתו תרומה

So the reason [why they belong to the neighbour] is that the owner has given up hope, but ordinarily they would not [belong to the neighbour]?<span class="x" onmousemove="('comment',' In regard to an ordinary loss, of which the owner is not likely to have become aware at once, it would not be said that it belongs to the finder. This would contradict the view of Raba. ');">⁸</span> Here we deal with a case where [the owner] is able to retrieve them.<span class="x" onmousemove="('comment',' So that ordinarily the owner never gives up hope and there is not even 'anticipated abandonment'. Thus there is no contradiction to Raba. ');">⁹</span>

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