(Mishnah): If one of the sisters was an Ervah to (e.g.) Reuven, he is forbidden to her and permitted to her sister. Shimon (the other surviving brother) is forbidden to both;

If a sister is forbidden to a brother due to an Isur Mitzvah or Isur Kedushah, she does Chalitzah but not Yibum;

If one [sister] was an Isur Ervah to one brother, and the second [sister] was an Isur Ervah to this (the other) brother, the one forbidden to this [sister] is permitted to the other, and the one forbidden to this is permitted to the other.

This is what was said 'when her sister is her Yevamah, she does Chalitzah or Yibum.'

(Gemara): If [Reuven] raped a woman, and she gave birth to a daughter (Dinah), and [Dinah] married his brother (Shimon), and she has a maternal sister (Sarah) from another man, married to a second brother (Levi), and [Shimon and Levi] died, [Reuven] is forbidden to his daughter and permitted to her sister.

This is the case of his daughter, in which 'her sister is her Yevamah, she can do Yibum.'

(Mishnah): If one [sister] was an Isur Ervah to this...

If [Reuven] raped a woman (Esther), and she gave birth to a daughter, and his brother (Shimon) raped [Esther], and she gave birth to a daughter, and both [daughters] married two paternal brothers [of Reuven and Shimon], but not [only] maternal brothers [and their husbands died], this one (Reuven) is forbidden to his daughter and permitted to her sister, and this one (Shimon) is forbidden to his daughter and permitted to her sister;

This is 'the one forbidden to this is permitted to the other, and the one forbidden to this is permitted to the other.'

(Mishnah): If two of three brothers were married to sisters, or to a woman and her daughter or granddaughter, (if the married brothers died,) the Yevamos do Chalitzah but not Yibum;

R. Shimon exempts [from Chalitzah].

If one of the sisters was forbidden to a Yavam due to Ervah, he is forbidden to her and permitted to her sister;

If one of the sisters was forbidden to a Yavam because of Isur Mitzvah or Kedushah, they do Chalitzah, but not Yibum.

R. Shimon exempts.

(Gemara - Ula bar R. Yishmael): So explained R. Hoshayah, the father of the Mishnah - R. Shimon exempts the second [to fall] from Chalitzah or Yibum. (Due to Zikah, it is as if he did Yibum with the first.)

(R. Yochanan): The group [that learns in the Yeshivah] asked, it never crossed the mind that one can acquire two sisters at once!

(R. Chanina, in front of R. Mana): [The group] argues [with R. Hoshayah. They hold that both are exempt.]

Question: [According to R. Hoshayah,] why does R. Shimon exempt the second from Chalitzah or Yibum?

Answer #1: [When the first fell, there was proper Zikah; it is as if he acquired her. When the second fell,] it never crossed the mind that one can acquire two sisters at once! (Since Yibum does not apply to her, she is exempt also from Chalitzah. Even though now, also the first cannot do Yibum, since initially she needed Chalitzah or Yibum, she still needs Chalitzah.)

There (in Bavel), they say that R. Shimon holds that Zikah does not take effect in a place of Zikah. ('It never crossed the mind that one can acquire two sisters at once' applies only when they fell at once.)

Answer #2 (R. Ba citing R. Lazar): [R. Shimon exempts the second] only if he transgressed and had Bi'ah [with the first. We explained this like YERUSHALMI TZERUFAH.]

Question: What is the law if someone from the market (a stranger) was Mekadesh the second?

Answer: According to Rabanan, it is full Kidushin (for she does not need Chalitzah). According to R. Lazar, the Kidushin is contingent - when [the Yavam] will have Bi'ah with the first, Kidushin will take effect on the second.

If [the Yavam] had Bi'ah with the second - According to Rabanan, it is Bi'as Ervah (due to Zikah, she is like Eshes Ach, and the child is a Mamzer). According to R. Lazar, it is not Bi'as Ervah.

If the first [sister] died - according to Rabanan, he is forbidden to the second. According to R. Lazar he is permitted to the second. (We explained this like SHA'AREI TORAS ERETZ YISRAEL.)

If the first [sister] had a Tzarah, he does Yibum with the Tzarah, and keeps his wife. He is forbidden to the second (sister, even though the first sister is no longer Zekukah).

Question #1: One is permitted to Achos (the sister of) the Tzarah of Chalutzaso (even though he is forbidden to Achos Chalutzaso. Also here, he should be permitted to Achos Tzaras Ishto, even though he is forbidden to Achos Ishto!)

Question #2: [Since he will need to do Chalitzah to the second sister,] he should be forbidden to the Tzarah, for [she will be] the Tzarah of Achos Chalutzaso!

Answer (R. Yudan): Had he wanted to have Bi'ah with the Tzarah [even] before he did Yibum (and uprooted Zikah from her sister), was he not permitted?!

Is he permitted at the beginning, and forbidden at the end (after he does Chalitzah)?! If you say so, it turns out that he makes an [Isur] Tzarah after death, but there is no Tzarah after death! (We explained this like RIDVAZ 17b.)

Question: R. Shimon contradicts himself! There (Mishnah 10, in which Reuven, Shimon and were married to unrelated women. Reuven died. Shimon gave a Ma'amar to the Yevamah, and then he died. R. Shimon) says that Levi may do Yibum with whichever he wants, and Chalitzah to the other. (He cannot do Yibum with both, for perhaps Yesh Zikah, and it is as if both fall from Shimon. After Yibum with one, he must do Chalitzah to the other, for perhaps Ein Zikah, and the first fell from Reuven, so one does not exempt the other.) And here he says so (the second is exempt from Chalitzah, for Vadai Yesh Zikah)?!

Answer #1 (R. Ze'ira): When I was there (in Bavel), I heard the reason. There, Zikah of two brothers (when the first fell, either could do Yibum) is not [proper] Zikah, and it does not take effect where there is a Ma'amar [which makes Safek Kinyan. Therefore, Levi does Yibum with whichever he wants, and Chalitzah to the other];

However, here, there is Zikah of one brother, and Zikah [of the second to fall] does not take effect on Zikah.

Answer #2 (R. Masniyah): What is the comparison of sisters to strangers? (Really, Yesh Zikah. Regarding strangers, both fall from Ba'al ha'Ma'amar, and one is exempted through Yibum of the other, just Chachamim decreed lest people say that when two fall from two brothers, Yibum of one exempts the other. Regarding sisters, the second does not fall, because due to Zikah, it is as if the first did Yibum.)

Question: If you want to ask [a contradiction in R. Shimon], ask about what R. Ze'orah cited R. Sheshes there, that R. Shimon says that [if Ploni gave a Ma'amar and then a brother was born and Ploni died], both [of Ploni's wives] are forbidden;

R. Shimon contradicts himself! There he says that both are forbidden (because Ba'alas ha'Ma'amar is acquired partially), and here (the Mishnah of brothers married to strangers) he says that both are permitted (he may do Yibum with either! We could have answered that there, there was Zikah of one brother, and here, there was Zikah of one brother.)