According to Rabah, if Reuven gives Shimon a gift, he can retract even after the Kinyan has been made, as long as they have not yet stood up following the transaction - because the Kinyan is made on the understanding that as long as they are still sitting, he will be able to reflect whether he is able to clinch the gift, or whether to make any further stipulations.

Rabah cannot be referring to a Matnas Shechiv-M'ra - because a Matnas Shechiv-M'ra does not require a Kinyan.

Rav Yosef holds that once they switch to a different issue, the donor can no longer retract, even if they have not yet stood up.

Rav Yosef tries to prove his opinion from Rav Yehudah's Din ('Sheloshah she'Nichn'su Levaker es ha'Choleh'), assuming that he is speaking about a Shechiv-M'ra who is only distributing part of his property) - because, according to Rabah, how can the three men issue a ruling immediately? Why do we not suspect that the Shechiv-M'ra will retract before they stand up?

Rav Ashi in the presence of Rav Kahana, used Rav Yosef's argument against Rav Yosef himself - inasmuch as, even according to him, why are we not concerned that he will retract before they have switched to another topic?

Rav Ashi himself answers both Kashyos with one sweep however ...

... his Kashya on Rav Yosef - by establishing the three men's final ruling only after they have changed the topic of conversation.

... Rav Yosef's Kashya on Rabah - by establishing it where they have already stood up before sitting down a second time in order to convey the Shechiv-M'ra's decisions to the heirs.

In spite of the principle that when Rabah argues with Rav Yosef, we rule like Rabah - in this case we will rule like Rav Yosef, due to the declaration that the Halachah is like Rav Yosef in three cases (all in this Masechta); 'be'Sadeh' (in the first Perek), 'Inyan' (our case), and 'Mechtzah' (in 'Mi she'Meis')'.

In spite of having listed 'ha'Ish es Imo, ve'ha'Ish es Ishto' in the category of 'Nochlin ve'Lo Manchilin', the Tana nevertheless sees fit to add 'ha'Ishah es B'nah ve'ha'Ishah es Ba'alah' in the category of Manchilin ve'Lo Nochlin' - to compare the two Halachos, to teach us that just as a man does not inherit his wife in the grave (i.e. he only inherits what she had in her possession when she died, as we learned earlier), so too does a son not inherit his mother in the grave (i.e. if he died before his mother, he does not pass on property that his mother leaves upon her death, to his heirs).

Those who inherit ...

... a man who dies if his married daughter (his only child) died before him are - his heirs (and not her husband).

... a woman who dies if her husband and children died before her are - her father's heirs (and not her husband's).

Despite the fact that this latter Halachah appears to be obvious (because there is no conceivable reason to even think that a son who dies before his mother should inherit her), we need the Mishnah to teach us this - because we would otherwise have explained the two Pesukim "ve'Lo Sisov" by Hasavas ha'Ben, one when his mother died before him, and the other, when he died before his mother (a 'Gezeiras ha'Kasuv' that a son inherits his mother 'ba'Ra'uy').

And the Tana only adds the third case (in the category of 'Manchilin ve'Lo Nochlin') 'Achei ha'Eim' (which we already know from 'B'nei Achos' [by Nochlin ve'Lo Manchilin], even though there is no Chidush) - because of the other two cases (where there is).

The Tana also sees fit to insert both 'ha'Av es ha'Banim' and 'ha'Banim es ha'Av' in the Reisha (in the case of 'Nochlin u'Manchilin'), even though the latter is self-understood from the former - because he wants to explicitly record all the cases.

We do not find it necessary to pose this Kashya, like we do on the Seifa - because the Reisha, unlike the Seifa, is not in itself, superfluous.

Rebbi Yochanan in the name of Rebbi Yehudah b'Rebbi Shimon made two statements: that a father inherits his son - and that a mother inherits her son.

It is obvious that a father and mother - also inherit their daughters.

We reconcile this ruling with the principle 'Mishpachas Eim Einah Keruyah Mishpachah' - by restricting the latter to giving Mishpachas Av precedence over Mishpachas Eim, so that in our case, it is only where her husband is no longer alive that a mother will inherit her son and daughter.

The reason that we quote 'Rebbi Yochanan Mishum Rebbi Yehudah b'Rebbi Shimon' rather than 'Amar Rebbi Yehudah b'Rebbi Shimon' - because the latter was not Rebbi Yochanan's Rebbi Muvhak (from whom he learned most of what he knew [see Gilyon ha'Shas]).

Rebbi Yehudah b'Rebbi Shimon learns his second ruling from the Pasuk in Masei "ve'Chol Bas Yoreshes Nachalah mi'Matos", from the word "mi'Matos" which pertains to both a woman's father and her mother (as we learned earlier), and which he treats as a regular 'Hekesh').