1) "MA'AMAR" WITH THE SECOND YEVAMAH AFTER "BI'AH" WITH THE FIRST
QUESTION: The Gemara explains that when the Mishnah states, "Ein Achar Chalitzah Klum," it also means "Ein Achar Bi'ah Klum." In a case in which the Yavam did Bi'ah with the first Yevamah and Ma'amar with the second Yevamah, the Yavam does not need to give a Get to annul the Ma'amar with the second Yevamah. Once Bi'ah is done with one of the Yevamos, nothing done afterwards takes effect.
The Gemara earlier (11a) teaches that when a Yavam does Yibum with one of the Yevamos, the remaining Tzaros become prohibited to him with only an Isur Aseh. Since Kidushin takes effect between a man and a woman who are prohibited to each other with only an Isur Aseh, the Ma'amar (which is an act of Kidushin) should take effect with the second Yevamah even after Bi'ah was done with the first!
Even though the Gemara (52b) says that the Mishnah follows the view of Rebbi Akiva who maintains that Kidushin does not take effect with a woman who is prohibited to the man with an Isur Lav (and thus Ma'amar does not take effect after Chalitzah is done because of the Isur Lav which prohibits the Yavam to the Tzarah of the woman who did Chalitzah), Rebbi Akiva should agree that in the case of Ma'amar after Bi'ah, the Ma'amar should take effect. Since, after doing Bi'ah with the first Yevamah, there is only an Isur Aseh against marrying the second Yevamah, Ma'amar with the second Yevamah should take effect.
ANSWERS:
(a) According to one opinion in Kesuvos (29b), Rebbi Akiva maintains that Kidushin does not take effect for any forbidden union, even with an Isur Aseh. Hence, when the Gemara here says that the Mishnah follows the view of Rebbi Akiva, it means that Kidushin does not take effect even with an Isur Aseh. (See ROSH 5:6.)
(b) However, the TOSFOS YESHANIM (11a), the RAMBAN in Kesuvos (29b) and other Rishonim there cite this Gemara as proof that the Tzarah of one's Yevamah is prohibited not only with an Isur Aseh but also with an Isur Lo Ta'aseh. That Isur is the prohibition of "Lo Yivneh," a Lo Ta'aseh which states that "Keivan she'Banah, Shuv Lo Yivneh" ("since he has built one house through Yibum, he may not build another one"), and it is not an Isur Aseh ("Bayis Echad Hu Boneh, v'Eino Boneh Shnei Batim" -- "he must build one house through Yibum, and not two"). Since the Yavam did Yibum with one Yevamah and not the other, it was as if he sent away the other one with Chalitzah.
Although the Gemara (44a) seems to support Rashi's view that the Isur of Bi'ah with two Yevamos is an Isur Aseh ("Bayis Echad Hu Boneh"), the ME'IRI (11a) explains that the Gemara does not mean to say that this verse is the source for the Isur. Rather, the Gemara's intention is merely to explain what the Isur is. The source for the Isur is the Lo Ta'aseh of "Lo Yivneh."

53b----------------------------------------53b

2) UNNECESSARY CASES IN THE MISHNAH
QUESTION: The Gemara questions the Mishnah which states "Ein Achar Chalitzah Klum" with regard to one who gives a Get after he does Chalitzah. The Gemara asks that the Get obviously is ineffective, because Chalitzah was already done.
The Gemara responds, "And according to you (ul'Ta'ameich) -- how do you understand the end of the Mishnah which says that when Ma'amar was done after Bi'ah, nothing is needed to annul the Ma'amar?" When Yibum (Bi'ah) was already done, Ma'amar obviously is ineffective!
The words of the Gemara are difficult to understand. If the Gemara is questioning the Mishnah's inclusion of the case of "Chalatz v'Nasan Get" and the case of "Ba'al v'Asah Ma'amar," why does it question the Mishnah at this point, when it discusses the end of the Mishnah? Those cases appear in the first part of the Mishnah (as Rashi on the Mishnah explains), and thus the Gemara should ask these questions earlier, when it explains the first part of the Mishnah. (MAHARSHA)
ANSWER: The MAHARSHA answers that the Gemara at this point does not initiate a new discussion on the Mishnah. Rather, it is a continuation of the previous discussion. (Accordingly, the colon should be deleted from the text of the Gemara. There should be no separation mark between this Sugya and the previous one.) The preceding Gemara records a dispute between Rebbi Yochanan and Reish Lakish about the status of the prohibition of the other brothers to the Yevamah with whom one brother did Chalitzah. Rebbi Yochanan says that she is prohibited to them with a Lav, and Reish Lakish says that she is prohibited to them with Kares.
The Gemara attempts to prove the view of Rebbi Yochanan from the Mishnah. The Mishnah adds that the law of "Ein Achar Chalitzah Klum" applies to a case of two Yevamos. According to Reish Lakish, there is no reason for the Mishnah to mention this; it is obvious that the Yavam who did Chalitzah with one of the Yevamos is Asur b'Kares to the others, and thus anything he subsequently does with the others (such as Ma'amar) will not take effect. According to Rebbi Yochanan, however, the Mishnah needs to mention this case in order to teach that although the Tzaros are prohibited to him with only an Isur Lav, nothing takes effect with them. (The Mishnah expresses the view of Rebbi Akiva who maintains that Kidushin does not take effect with an Isur Lav.)
Reish Lakish responds that the Mishnah indeed does not need to mention that "Ein Achar Chalitzah Klum" applies to a case of two Yevamos. It mentions this case only to maintain parallel structure with the first part of the Mishnah, which mentions all of the possible scenarios in each case (with one Yevamah and with two Yevamos). Reish Lakish asserts that even according to Rebbi Yochanan, the Mishnah may include a case only for the sake of consistency. According to Rebbi Yochanan, there is no reason for the Mishnah to mention that Ma'amar does not work after Bi'ah in a case of two Yevamim who do Bi'ah and then Ma'amar with one Yevamah. When the second Yavam does Ma'amar, the woman is already an "Eshes Ish," and obviously the Ma'amar cannot take effect. It must be that the Mishnah mentions that case only for consistency. Similarly, the Mishnah mentions the case of Ma'amar after Chalitzah only for consistency.
The Gemara continues with another attempt to prove the opinion of Rebbi Yochanan. The Gemara says that even in the first part of the Mishnah, which discusses cases of one Yavam with one Yevamah, the Mishnah mentions an obvious law -- "Chalatz v'Nasan Get," a Get does not take effect after Chalitzah. According to Reish Lakish, who says that all of the cases are mentioned only because of the first case of one Yavam with one Yevamah, there is no reason for the Mishnah to mention "Chalatz v'Nasan Get" with one Yevamah if it does not teach anything new. According to Rebbi Yochanan, however, who maintains that the Mishnah needs to teach that the law of "Chalatz v'Nasan Get" applies to a case of two Yevamos, the Mishnah mentions "Chalatz v'Nasan Get" in the case of one Yevamah as well in order to maintain consistency with the second part of the Mishnah.
Reish Lakish responds that "even according to you, Rebbi Yochanan, what is the point of mentioning the law of 'Ba'al v'Asah Ma'amar' in the case of one Yavam with one Yevamah?" Even according to Rebbi Yochanan, there is no need for the Mishnah to teach that law in the case of one Yevamah or in the case of two Yevamos! The Gemara answers that the Mishnah nevertheless mentions that case in order to parallel the scenario of "Chalatz v'Asah Ma'amar," which the Mishnah does need to mention.

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