Question: If a Shechiv Mera (one who fears lest he die from his illness) gave a gift, until when can he cancel it?

Answer #1 (Rabah): He can cancel it as long as the parties are seated.

Answer #2 (Rav Yosef): He can cancel it as long as they are engaged in the Kinyan.

Support (Rav Yosef, for himself): Rav Yehudah taught that if three men came to visit a sick man, they may write down his command, or execute it, whichever they want.

If he can cancel a Kinyan as long as they are sitting, why can they execute his command? Perhaps he will cancel it!

Rejection (Rav Kahana): Rav Yehudah opposes also Rav Yosef. Why can they execute his command? We should we be concerned lest the sick man retract!

Rav Yosef must say that they execute the command only after the sick man begins a new matter.

Rabah can similarly answer that they execute it only after they leave where they were sitting!

The Halachah follows Rav Yosef regarding a field (12b), (beginning) a (new) matter (our law), and one who gives half his property to his wife and sons (143a). (Everywhere else (Tosfos - in Bava Basra) that Rabah argues with Rav Yosef, the Halachah follows Rabah.)

(Mishnah): A woman bequeaths to her son (and does not inherit him)...

Question: Why was it needed to teach this? We already learned that a son inherits his mother, but does not bequeath to her!

Answer: This teaches that a mother bequeaths to her son like to her husband;

Just like a husband does not inherit his wife when he is dead (to cause her property to pass to his heirs), also a son does not inherit his mother after his death to bequeath to his paternal brothers.

(R. Yochanan citing R. Yehudah b'Rebbi Shimon): Mid'Oraisa, a father inherits his son and a mother inherits her son, for it says "Matos";

This equates the tribes of the mother and father. Just like the father inherits the son, also the mother.