Gemara

151b (Rav Nachman): Shmuel taught that anyone who could retract if he recovered, he can retract even if he did not recover. He can take back the property for himself, or give it to someone else?!

(Rava citing Rav Nachman): A partial Matanas Shechiv Mera (he kept some property) is totally like a gift of a healthy person. If the giver recovers, he cannot retract, and it requires a Kinyan.

Question (Rava - Mishnah): If a Shechiv Mera gave a gift, and kept some property, if he recovers, he cannot retract (even if no Kinyan was made)!

Answer: No, a Kinyan was made.

Question (Rava - Seifa): If he did not keep any property, if he recovers, he can retract. (If a Kinyan was made, why can he retract?)

Answer (Rav Nachman citing Shmuel): If a Shechiv Mera gave all his property to others, even if they acquired from him, if he recovers, he can retract. Surely, he gave only because he expected to die.

The Halachah is, a partial Matnas Shechiv Mera needs a Kinyan, even if he died. One who commanded (to give) due (expectation of) death does not need a Kinyan, as long as he died. If he recovered, he can retract, even if a Kinyan was made.

152b (Rav Dimi): A Daitiki (document of a Matnas Shechiv Mera) nullifies a previous Daitiki (because it shows that the giver retracted).

Version #1 - Chachamim of Sura - (Rav): If Reuven wrote a document and was Mezakeh for Shimon and then wrote and was Mezakeh for Levi, Shimon acquires;

(Shmuel): Levi acquires.

Rav holds that (because he was Mezakeh,) this is like a gift of a healthy person. Shmuel holds that it is a Matnas Shechiv Mera.

Question: They already argued about this, i.e. a Matnas Shechiv Mera that says that a Kinyan was made!

Answer: Had they argued only there, one might have thought that only there Rav considers it like a gift of a healthy person, because a Kinyan was done. Had they argued only here, one might have thought that only here Shmuel argues, because no Kinyan was done.

Version #2 - Chachamim of Pumbadisa - Question (Bei Rav): If Reuven wrote a document and a Kinyan was done, what is the law?

Answer (Shmuel): One cannot retract after a Kinyan.

Rabanan understood that he cannot retract to give to someone else, but he can retract to keep the property himself.

(Rav Chisda): He cannot retract even to keep the property himself.

Rishonim

Rif: The Halachah is, a partial Matnas Shechiv Mera needs a Kinyan, even if he died. One who commanded due death does not need a Kinyan, as long as he died. If he recovered, he can retract, even if a Kinyan was made.

Rambam (Hilchos Zechiyah 9:15): If a Shechiv Mera (Ploni) wrote a document for Shimon, and then wrote for Levi, Levi acquires, for Ploni can retract until he dies. This is whether he gave all or part of his property. He can take back the property for himself, or give it to someone else. Even if he wrote and was Mezakeh to Shimon, and wrote and was Mezakeh to Levi, Levi acquires. Even if a Shechiv Mera was Mezakeh, it is a Matnas Shechiv Mera.

Rambam (16): If a Shechiv Mera wrote and was Mezakeh and did a Kinyan, nothing can undo the Kinyan. He cannot retract to give to another or for himself, whether he gave all or part of his property.

Magid Mishneh: Nothing can undo the Kinyan if there was also Zechiyah. If only Kinyan or Zechiyah was done, he can retract. If he commanded due to death, even if he did both, he can retract. The Rashbam explains that Zechiyah was through giving the document. The Ge'onim say that he said 'go make a Chazakah.'

Rosh (9:31): Shmuel taught that if a Shechiv Mera gave all his property to others, even if they acquired from him, if he recovers, he can retract. Surely, he gave only due to death. This implies that if he did not recover, he could not retract. This is when he gave the recipient Yifuy Ko'ach (greater rights). If the recipient received the document before the giver died, we do not require that he gave Yifuy Ko'ach. This is if the document was written like a command ('give to Moshe...') If it was written like a gift ('my field is given to...'), the giving of the document is a Kinyan. It is like a Matnas Shechiv Mera with a Kinyan, which requires Yifuy Ko'ach. If there was no Yifuy Ko'ach, he does not acquire. The Kinyan done in his lifetime does not help after death, when the gift must take effect. Shmuel holds that since Matnas Shechiv Mera does not require a Kinyan, and he did a Kinyan, he showed that he wanted the recipient to acquire at the time (after death) only through a Kinyan, and then a Kinyan does not work.

Rosh (ibid.): The Rashbam explains that 'wrote and was Mezakeh' means that he wrote the document and gave it to the recipient. This is difficult. If so, how could Rav say that the first acquires? In Bava Metzia (19a), we say that a Shechiv Mera can retract, even if he commanded to give the document. A latter Daitiki nullifies a previous one, even if the first was given! The Rivam explains that 'wrote' means that he wrote the document and gave it to the recipient. 'Wrote and was Mezakeh' means that he wrote and gave the document, and was Mezakeh through someone else (Yosef). If they were Metaltelim, he gave them to Yosef to acquire for Moshe. If it was land, Yosef did Chazakah for Moshe. The Zechiyah was written in the document. This is the Matnas Shechiv Mera with a Kinyan that they argued about earlier! We must say that there was Yifuy Ko'ach, for if not, Shmuel holds that even the latter does not acquire.

Poskim

Shulchan Aruch (CM 250:13): If a Shechiv Mera (Ploni) wrote to David, and then to Moshe, Moshe acquired, for Ploni can retract until he dies. This is whether he gave all or part of his property (Rema - (if he gave part, it is only) if he specified that it is a Matnas Shechiv Mera).

Beis Yosef (DH u'Mah she'Chosav Rabeinu b'Shem): The Rambam says that a Shechiv Mera can retract even from a partial gift. The Tur questioned this, for a partial gift is totally like a healthy person's gift, and it cannot be retracted! We can say that he can retract when he specified at the time that he gives it like a Matnas Shechiv Mera, like the Rambam said in Halachah 8:17.

SMA (40): The Rambam could hold like Tosfos (152b Sof DH Matnas), that the same applies to a partial gift.

Drishah (23): Tosfos holds that according to Shmuel, even though a Matnas Shechiv Mera requires a Kinyan, it did not need to be written in the document. Since he wrote it, perhaps this shows that he intended that to give only through the document, and it cannot be after death. Also the Rambam can say that this makes it like a healthy person's gift.

SMA (41): The Tur (Sof 125, citing the Ramah) says that the giver cannot retract once he gave it to a Shali'ach. We must say that that is when he commanded to give it immediately. Since he did so much to remove it from his Reshus, he can retract. Here, he said not to give it until he dies.

Question (Taz DH Bein): Here, he only wrote it! If the SMA refers to the Seifa (the continuation of this Halachah in the Tur (and Shulchan Aruch), in which he was also Mezakeh, the SMA's answer does not apply (for surely, he was Makneh to acquire immediately)! However, it is difficult to resolve the Seifa with Siman 125, in which we say that even if a Shechiv Mera said 'bring it to Ploni', it is as if he said 'acquire for me.' Here we say that Zechiyah even with a document does not help!

Shulchan Aruch (ibid): He can retract to keep for himself, or to give to another. Even if he wrote and was was Mezakeh for David and wrote and was was Mezakeh for Moshe, Moshe acquires, for if a Shechiv Mera was Mezakeh, it is still a Matnas Shechiv Mera.

SMA (43): The Tur says that the latter gets it only if he was given Yifuy Ko'ach. The Shulchan Aruch and Rema omitted this, for they require this only if he gave Yifuy Ko'ach to the first.