Using a lost item that was switched

Shalom.

A child was sent to kindergarten with a sweater and did not bring it back, and when they came to look for it, they found a sweater that is exactly the same, identical in every way, but they can tell that it is not theirs. Is it permitted to take it?

Shalom u-vracha.

It is reasonable to assume that the owners of the remaining sweater took the one belonging to those who are looking for it, and therefore it is permitted.

In siman 136, se’if 2, there is a dispute between the Taz and the Ketzot HaChoshen regarding a person who gave a garment to a launderer and received in return the garment of another person, whether he may use it. The Taz writes that if it remained in his possession for a long time, we may assume that the owner has despaired (ye’ush), and the launderer compensated him with something else. The Ketzot disagrees and argues that this is a case of ye’ush after a change of domain (shinui reshut), which is not effective. The Netivot reconciles the words of the Taz by explaining that since no public “noise” was heard about the matter, it is assumed that the garment remained a long time in the launderer’s hands and the owner despaired before it came into this person’s possession. Therefore, in any case where it remained for a long time before coming to him, he may certainly take it according to all opinions.