Question: It says below (137b) "take this Esrog for a gift on condition that you return it to me", if he returned it he was Yotzei, even though he cannot be Makdish it!

Since he said "to me", he means "that is proper for me", like it says below. (He cannot use Hekdesh!)

Answer #1: There, he can be Makdish it for as long as it is in his hand, so others will not benefit from it. Here, he could not be Makdish it at all.

Answer #2 (Ri): The gift does not depend on Hekdesh. Even if he cannot make it Hekdesh, it is a gift;

The Gemara means as follows. Any gift... i.e. it is weak like this, that he gave it only in order that his father will eat;

He was not precise to say that if he was Makdish it, it is not Mekudeshes, for he could not do anything from it. He gave it only in order that his father eat, like it says in Nedarim (48a) according to one version that the Seudah proves about it;

It mentioned if he was Makdish it only because in the episode, this occurred (the recipient was Makdish it). If according to the version that explains there because Vitur (matters that people normally pardon) is forbidden regarding Mudar Hana'ah (one who is forbidden to benefit due to a vow), and normally, even though he cannot make it Hekdesh, it is a gift.

Support: The Yerushalmi connotes like this. It says about that case, that any gift that if he made it Hekdesh...

R. Yirmeyah asked "if so, one cannot give a gift to his friend on condition that he not make it Hekdesh...!"

It says that our Mishnah means that any gift that is like the episode in Beis Choron, which was a scheme, is not a gift.

Explanation: Obviously he is not believed about property that fell to him when he is Goses.

Implied question: Regarding Bechorah he is believed!

Answer: That is because he is proper to inherit him, for it is known that he is his son. However, here that we do not know whether or not he is proper to inherit him, he is not believed.

Implied question: This is not a [full] Migo. If he would divorce her, she would be disqualified from Kehunah. Now that he says "this is my son", he does not disqualify her!

Answer: In any case, it is considered a Migo to exempt her from Yibum.

Explanation: We do not say "since he could divorce her" (he is believed to say that he is his son).

One might have thought that now, he is not believed to say "I divorced my wife now." Even for the future he is not believed to say "I divorced my wife."

Question: If so, in our Mishnah why is he believed to say "this is my son"?

Answer: Only regarding saying "I divorced her" [R. Yochanan] did not say [that he is believed] through a Migo, since he could divorce her, for had he truly divorced her, it would have publicity. Therefore, he is not believed;

However, to say "this is my son" he is believed through a Migo, since he could divorce her, for it could be that he has a son, and people do not know about this.

Question: What is the Chidush? Obviously, he is not believed to say retroactively "I divorced my wife", for if he were believed, how did Chachamim's enactment to write the date on a Get help, so he will not cover up for his sister's daughter if she will be Mezanah while married to him (Gitin 17a)?

Note: If one could write a Get without a date, if he did so and gave it to her, Beis Din could not kill her (unless they could find the witnesses and they would say that the Zenus preceded the Get). The same applies to covering up for any wife, just normally a man would not want to save a wife who betrayed him. A sister's daughter is different, for he is very fond of her.

Still he will cover up for her. He will say "I divorced her before the Zenus", and he will be believed!

Partial answer: Granted, according to the opinion below we do not divide his words, this is fine, He needs to teach that even from now and onwards he is not believed when he says "I divorced her beforehand";

However, according to the opinion below we divide his words, he is believed from now and onwards. Only retroactively he is not believed. This is difficult, for this is obvious!

Reference: Rava's teaching is in Sanhedrin (10a). It says there "one might have thought that we say that a person is a relative to himself (so we totally ignore testimony that he said about himself), but we do not say so about his wife. [Rava] teaches that this is not so.

Question (R. Chayim): Obviously, one is a relative regarding his wife, like the Mishnah in Sanhedrin (27b)!

Answer: Even though he is disqualified from testifying about his wife, when he says "Ploni had Bi'ah with my wife", one might have thought that since he is believed about Ploni, he is believed also about her.