Siman 175

The Sages, of blessed memory, said (30a): Any yevamah of whom I cannot read at the time of falling "her yavam shall come upon her," she is like the wife of a brother who has children and is forbidden. The explanation of these matters: any yevamah who is not fit for yibbum at the time of falling because of a prohibition of ervah is forbidden to him forever, even if the prohibition is removed. For example, two brothers who are married to two sisters, and one of them died and his wife fell before the second, and she is an ervah to him because of being his wife's sister—even if his wife died afterwards, such that he is permitted to her sister after her death, even so she is forbidden, and he is liable for karet for her. This is because at the time of falling she was an ervah to him. And the reason for the matter is that a brother's wife is an ervah, except that when he dies without children the Torah permitted her to him; and since at the time of falling she was an ervah to him because of another prohibition of ervah, the prohibition of a brother's wife remains in its full force, so that even when the other prohibition is removed, this prohibition of a brother's wife remains.

And it is not only necessary to state this in a case where at the time of her falling for yibum she was permitted to the market, but even if she was bound to this house, such as if they had a third brother to whom she was not an ervah and he performed yibum, and even if afterwards the wife of this one who was married to her sister died, and afterwards the third brother died—which would be two points in her favor, as this woman was also bound to this house the first time, and also now at the time of her falling from the third brother for yibum to this second brother his wife had already died and she fell before him in a permitted state—nevertheless, since at the first time she fell before him in a state of prohibition, her law is like a brother's wife who has children, and she remains in her prohibition to him forever. And even if his wife died before the third brother married her sister, she is nevertheless prohibited to him for the reason that has been explained. And not only this, but even her tzara has the law of the tzara of an ervah; for example, if the third brother had another wife who was not an ervah to him, he is also prohibited to the tzara just as with the tzara of an ervah, for it is one and the same reason: since she remains from the first falling under the prohibition of a brother's wife, her law is forever like an ervah who also prohibits her tzara, and likewise the tzara of her tzara, and always according to the law that was explained regarding an ervah in siman 173.

And not only regarding a prohibition do we follow the time of her falling [into zika], but even regarding permission: if at the time of falling she was permitted to him, even though she was subsequently prohibited to him, if the prohibition was removed, he is permitted to perform yibbum with her because at the time of falling she was permitted to him. How so? Three brothers, two of whom are married to two sisters, and one of them died and his wife became bound to the third who is not married to her sister, and he did not manage to marry her before the second brother died who was married to the other sister, and consequently now both of them are prohibited to the third, for behold, two sisters stand before him in zika. If the wife of the second brother died, the first returned to her permitted status even though she was prohibited in the interim, because she was permitted to him at the time of falling. But if the wife of the first died, the second is not permitted, for behold, at the time of falling she was prohibited to him; even though the prohibition is only due to zika, nevertheless she is prohibited forever (ibid.).

In a case where two sisters fell before him from two brothers, how should he act to permit them to the market? For to exempt them without anything is impossible, as she is not literally his wife's sister, since each one is only his zekukah and not his wife as long as he has not yet married her. Consequently, it is understood that he is obligated to perform chalitzah for both of them. However, if they have co-wives, he should perform chalitzah for the co-wives and not for the sisters, for the chalitzah of the sisters is a deficient chalitzah and they do not exempt the co-wives (27a), as I wrote in siman 170.

Regarding one before whom two sisters fell from two brothers, if there is another brother, there is a simple remedy so that the first may be subject to yibbum. That is, that one of the brothers shall perform chalitzah for the second, and the first will be permitted. For what does it matter to me if the second died or if she received chalitzah? Behold, even with chalitzah her zikah is removed, and the first returns to her permitted status. However, ab initio they forbade doing so as a decree, lest they perform chalitzah for the first and perform yibbum for the second, as not everyone knows the difference between one and the other. And this is a complete prohibition, for the second was forbidden at the time of falling, just as she is not permitted by the death of the first. But ex post facto, when they performed chalitzah for the second, the other brother is permitted to the first. And this is what the sages taught in the Mishnah (beginning of chapter 3): Four brothers, two of whom were married to two sisters, and those married to the sisters died—behold, these perform chalitzah and do not perform yibbum. And we do not say ab initio to perform chalitzah for the second and perform yibbum for the first because of the decree, as has been written (28a). And know that this which we said, that the first was permitted to undergo yibbum to the second brother, this is according to the one who holds that an invalid chalitzah does not need to go around to all the brothers to permit herself, as has been written in siman 170. For according to the one who holds that she requires chalitzah from all the brothers—and this is an invalid chalitzah, for she is the sister of his zekukah—once she performs chalitzah also from the second, how can he perform yibbum with her sister? Behold, she would be the sister of his chalutzah.

And so too, if there is one among the brothers for whom the first yebama is an ervah to him, and consequently he is permitted to the second, for she is not the sister of his zekukah since an ervah is not bound to him, and he performed yibbum with the second, the first has returned to her permitted status and one of the brothers is permitted to perform yibbum with her. But if for one of the brothers the latter is an ervah to him and he performed yibbum with the first, the latter remains in her forbidden status to all the brothers because she was forbidden at the time of falling, and she performs chalitzah with one or more according to the opinions explained in siman 170 regarding the law of a disqualified chalitzah. And if he did not perform yibbum with the first, he performs chalitzah to her, and all the rest of the brothers perform chalitzah to both of them and they may not perform yibbum because of the reason that has been explained.

Two brothers married to two sisters, and both died and it is not known which died first, and they have brothers, and it is impossible to perform yibbum with both of them because the zika falls upon both of them and each one is the sister of his zekukah, behold these perform chalitzah and do not perform yibbum, as has been explained. And even if one of them was forbidden to one of the brothers by a negative commandment or a positive commandment, and certainly by the prohibition of a sheniyah, they perform chalitzah and do not perform yibbum, for the prohibition of a negative or positive commandment does not push aside the zika. But if one of them was an ervah to one of the brothers, behold her sister is permitted to him; if he wishes he performs chalitzah, if he wishes he performs yibbum, for his zika did not fall upon both of them, as there is no zika upon an ervah. And there is a novelty in this law, that even though it is not known which died first, we do not say that after one has performed chalitzah the other shall be permitted, for perhaps she is the first and she would be a yevamah who was permitted and forbidden and returned and was permitted, and as we have written we do not say so since there is a doubt in the matter, for perhaps she is the last and it is like a doubt of Torah law, even though this is not the sister of his wife but rather the sister of his zekukah, because we hold that there is zika (see Tosafot 27b, beginning with "But").

This is the wording of the Tur and Shulchan Aruch: Four brothers, two of whom are married to two sisters, and those married to the sisters died at the same time or one after the other before they managed to perform yibbum for the first—both of them perform chalitzah and do not perform yibbum, for it is impossible for either of them to perform yibbum due to the prohibition of the sister of one's zekukah. If they went ahead and married, they are not removed from them. Thus far the wording of the Tur. And in the Shulchan Aruch, section 3, it is written in this wording: And if they went ahead and married, each one marrying one of the sisters, they are removed from them; and there is one who says they are not removed. Thus far his words. And in the Rambam at the beginning of chapter 7 it is written: if they went ahead and married, they are removed. And in truth, it is proven so in the Gemara (28a). And the words of the Tur are perplexing, and therefore there is one who says that it is a scribal error (Bach). But even the Rambam in the Commentary on the Mishnah also ruled that they are not removed, see there, and in his work he retracted. Therefore it appears that the Tur holds so, that they are not removed (and his reason is that even though according to what is explained at the beginning of chapter 3, the First Tanna holds they must remove them, and Rabbi Eliezer holds it is a dispute between Beit Shammai and Beit Hillel, yet in Eduyot chapter 5, Rabbi Eliezer counted it among the stringencies of Beit Hillel; and Abba Shaul in Yevamot (28a) holds that Beit Hillel are for leniency, and the Bartenura wrote there in Eduyot: in the Gemara in Yevamot we reverse it, etc., and such is the halachah, that if they went ahead and married, they shall remain. Thus far his words. And this is the system of the Tur; and see Tosafot Yom Tov at the beginning of chapter 3 of Yevamot, and delve into this).

According to the ruling of the Rambam, also in the previous law when it is not known who died first, also when they preceded and married, they are removed from them (the Maggid Mishneh). However, according to the Sugya of the Shas there, it is explained that from the second they do not remove, for since there is a doubt in the matter, perhaps the first performed yibbum with the second and he with the first, and it is a yevamah who was permitted and forbidden and returned and was permitted (Beit Shmuel, subsection 4).

They further wrote: if one of them was forbidden to one of the yevamin due to a prohibition of ervah, he is permitted to the second, for the ervah is not bound to him, and it results that only one is bound to him, while the second [yavam] is forbidden to both of them. If one of them was forbidden to this one due to ervah, and the second was forbidden to the second due to ervah, the one forbidden to this one is permitted to that one, and the one forbidden to that one is permitted to this one, for each one has only one bound to him. But if they are only forbidden to them by a negative commandment or a positive commandment, and certainly if it is a sheniyah, the zikah is not pushed aside from them, and they perform chalitzah and do not undergo yibbum. Thus far his words. And it is simple.

They further wrote: Three brothers, two of whom are married to two sisters, and one of the husbands of the sisters died, and afterwards the husband of the second sister died, and the second sister also fell before the third brother—both are forbidden to him, for they are rivals to one another in the zika, and they perform chalitza and do not perform yibbum (and we have already explained this). And if he performed maamar with the first, and afterwards her sister fell before him, he must release the one with whom he performed maamar with a get and chalitza, and the latter with chalitza. Thus far their words. And already in siman 170 the reasons for these matters were explained with the help of Heaven.

Three brothers, two of whom are married to two sisters and one is married to a stranger; the one married to the stranger died, and one of the husbands of the sisters performed yibbum with his wife and then died, and his wives fell before the second of the husbands of the sisters—the first one, who was married from before, is a complete ervah to him, and the second one, whom he had taken in yibbum, leaves on account of being the tzarah of an ervah, and they are exempt even from chalitzah. However, if he had not yet performed yibbum with her, even if he performed maamar with her, she requires chalitzah, for she is not yet the tzarah of an ervah; and she may not undergo yibbum even if he had not yet performed maamar with her, for she is the tzarah of a wife's sister through zika. And likewise in the reverse case, if first one of the husbands of the sisters died and afterwards the one married to the stranger died, she performs chalitzah and does not undergo yibbum for this reason.

The sages taught in the Mishnah (30.): Three brothers, two of them married to two sisters and one married to an unrelated woman; one of the husbands of the sisters divorced his wife, and the one married to the unrelated woman died, and the divorcer married her and died—this is what they said: and all of them who died or were divorced, their tzarot are permitted. Thus far his words. And they inferred in the Gemara: the reason is that the husband of the sisters divorced first and afterwards the one married to the unrelated woman died, so that even through zika she never became her tzara (Rashi); but if the one married to the unrelated woman died and afterwards one of the husbands of the sisters divorced and died, she is forbidden to the third.

And according to the approach of Rashi and Tosafot, specifically when the one who divorced married the stranger and died, then she is forbidden to the third brother because she was the rival wife of the forbidden relation before the divorce, and the zika is on account of the one who divorced; for if he did not marry her, the zika is not on his account but from his first brother. And even though she was also bound to the one who divorced, nevertheless, the power of the zika of the second when he dies is not as effective as the power of his zika during his lifetime, when each one was able to marry her (Maggid Mishneh chapter 6 in the name of the Rashba). And if it is difficult: in truth, why is he permitted to marry her, for is she not the rival wife of his wife's sister through zika? One can say that she is not considered a rival wife of a wife's sister through zika unless he married her and died, and both of them fell before the third brother on account of the second brother, but while he is alive, no (Tosafot). And the explanation of the matters is: how can we forbid the stranger to one of the brothers on account of the kinship of their wives, when she is only fit for one of them? Therefore, whoever married her, it is a sign that the stranger was bound to him from the death of the first. Therefore, when he divorced his wife after he married this one, the stranger was for one moment the rival wife of his wife, namely until the divorce; and automatically, when he dies afterward, this stranger is forbidden to the third because she was for one moment the rival wife of his wife's sister. However, in section 20 we explained another intention in this, see there.

And there is still a question regarding this: what does it matter that the stranger was the rival wife of his wife's sister until the divorce? For ultimately, when this second one died, she had already been divorced, and at the time of the second one's death, she was not the rival wife of his wife. And we hold that death causes the falling [for levirate marriage] and not the initial marriage. And behold, regarding the forbidden relation herself, if he divorced her and afterwards died, her rival wife is permitted to undergo yibbum, as is written in siman 173; and the zika of a forbidden relation is not more stringent than the forbidden relation herself.

And in truth, from the words of Rashi, of blessed memory, there, it is implied that what we said regarding one who wed and afterwards divorced, that she is forbidden, is not according to the conclusion where we maintain that death causes the falling [for levirate marriage], but rather according to the one who holds that the first marriage causes the falling. However, according to the halacha that death causes the falling, even in a case where he wed and afterwards divorced, she is permitted and is not forbidden to the third unless the second died and did not divorce his wife at all; for since we maintain there is zika, it is as if she comes also by way of the second. And even if the second did not wed, she is forbidden to the stranger, for she became the rival wife of his wife's sister through zika (so wrote Rashi regarding Rava there in the heading "This is etc." for Rava holds death causes the falling etc. Thus far his words. And so it is implied from the Gra in subsection 18, see there, and in the Beit Shmuel subsection 8; and the Tosafot Yom Tov there did not write so, see there and examine carefully):

But the Rambam, of blessed memory, in chapter 6, law 25, did not rule accordingly. This is his wording: Three brothers, two of them married to two sisters and one married to an unrelated woman; the one married to the unrelated woman died, and afterwards one of the husbands of the sisters died—behold, the unrelated woman performs chalitzah and does not undergo yibbum, because she is the rival wife of his wife's sister through the zika of his brother who died last. Not only that, but even if one of the husbands of the sisters divorced his wife after the one married to the unrelated woman died, and the divorcer died—behold, the unrelated woman performs chalitzah and does not undergo yibbum, since she became the rival wife of his wife's sister through zika for one moment; for if she were to undergo yibbum, perhaps he would come to perform yibbum with her even if this one who died last had not divorced his wife. And for what reason did they not decree this matter regarding marriage—for behold, the rival wife of an ervah in marriage, if he divorced the ervah and died, her rival wife is permitted to the yabam as I have written—because the prohibition of the rival wife of an ervah in marriage is known to all, and they will not come to permit the rival wife if he did not divorce the ervah; but the prohibition of the rival wife of an ervah through zika is not known to all, and they would come to permit the rival wife even when the ervah was not divorced. Thus far his words.

And he was not forced to this distinction, as one can distinguish simply: that regarding a forbidden relation, since he divorced her before she fell before the yavam, the divorce is effective for her, for when the rival wife falls before the yavam, she falls before him in a state of permissibility. But here regarding a stranger, since at the time of falling she fell before him under the prohibition of zika, divorce is not effective for her. And the Rif, of blessed memory, wrote this distinction in the third chapter, see there, for he wrote that this distinction is more logical than the previous distinction.

It appears to me that it did not seem correct to the Rambam to accept the distinction of the Rif, for indeed one must scrutinize, both according to their approach and according to the approach of Rashi, what prohibition exists regarding the hazarah to the third brother when the second did not marry her. For regarding the hazarah, even if he did not divorce his wife at all, in what way is she called the tzarah of a wife's sister through zikah? Behold, this second brother could have married her, and she would not have been forbidden to him by virtue of the fact that she was subject to the zikah of the tzarah of the wife's sister of the third brother. And likewise, the third brother could have married her, and she was not forbidden to him because of the zikah of the tzarah of the wife's sister of the second brother. And why now, when one of them died, by what is she forbidden to the remaining brother? And it is as I wrote in section 14, that the power of the zikah of the second brother when he is dead is no greater than the power of his zikah during his lifetime, for each one of them could have married her.

And it must be said that the reasoning is thus: certainly when both of them are alive, one of them is permitted to perform yibbum; but when the yibbum occurs after the death of one of them, the stranger appears like the zekukah of this deceased one, since this third brother delayed his yibbum until the second died and did not perform yibbum earlier, we learn from this that she was incumbent upon the second, and therefore this third one did not perform yibbum in his lifetime, and when he died he performed yibbum, and this is certainly like the tzarah of a wife's sister in zika (and this is the intent of the Tosafot mentioned in section 14, and not as was written there). And according to this, it is impossible to say the reasoning of the Rif that at the time of falling she fell before him with a prohibition of zika, for there is no prohibition of zika here as long as both of them are alive. Therefore, the Rambam required the first reason, because it is a light prohibition they might come to permit it even when he did not divorce; except that according to Rashi it is not prohibited unless he did not divorce her, and according to the Rambam even if he divorced her it is prohibited because of a decree lest they permit it even without a divorce.

And there are those of our teachers who hold that in truth, if this second one did not marry the forbidden woman and died, the third is permitted to return, even if the second did not divorce his wife at all, for the reason we wrote: that his power should not be greater in his death than in his life, for the third would have been able to perform yibbum with her. And the prohibition is only when the second married her and died, for then it is simple that if he did not divorce his wife, she is a complete co-wife of a forbidden relation. Rather, even if he divorced her, and even before the marriage of the forbidden woman, the forbidden woman is considered as her co-wife from the time of the death of the forbidden woman's husband; for because he performed yibbum with her afterwards, it was revealed that she was his zekukah. Therefore, even though regarding a complete forbidden relation, when he divorced her before his death the co-wife is permitted, nevertheless in this they were more stringent because she fell under the prohibition of the zikah of a wife's sister when the first died. And this is the opinion of the Ra'avad and the Rashba, of blessed memory, and they wrote that this is also the opinion of the Rif, of blessed memory, for his intention was specifically where he married her.

The Tur and the Shulchan Aruch, section 8, have another approach in all of this and they hold the opposite: that if the second brother married the zharah, even if he divorced his wife after he married her and died, the zharah is permitted to the third. Their reasoning is simple, just as we establish regarding every co-wife of an ervah, that when he divorced the ervah and afterwards died, her co-wife is permitted; and here too it is so, for since this second brother married the zharah, she has literally become the co-wife of an ervah regarding the third, and regarding this we learned: "and all of them, if their co-wives were divorced, they are permitted." And the prohibition is when he did not marry her and the husband of the zharah died before he divorced his wife; even if he divorced her afterwards and died, the zharah is forbidden to the third because the wife of the second, who is the sister of the wife of the third, was her co-wife in zika. Their logic is to distinguish between when both of them are alive and when one of them died, as I wrote in section 20, and with this all the opinions have been explained (and this is what the Tur and Shulchan Aruch wrote, "even if he did not marry the zharah etc.," which implies all the more so if he married her, it refers to where he did not divorce her at all; and the Tosafot Yom Tov wrote in vain that the words of the Tur contradict one another, and their intention is clear as I have written, and what he wrote from the Rosh is also no proof for his words are opaque, and delve into it).

Our teacher, the Rema, wrote that the same law applies if he was married to a stranger and has children, she is forbidden to him because of the zika of his brother's wife who has children. Thus far his words. This means: three brothers married to three women who are strangers to one another, and one of them has children, and the one who has no children died, and afterwards the one who has children died, the first woman is forbidden to the third. For as has been explained in the previous law, when two are married to two sisters and one to a stranger, and the one married to the stranger died, even though each of the brothers could have performed yibbum with her, nevertheless, if afterwards one of the husbands of the sisters died, the stranger also becomes forbidden to the third because she appears like the rival wife of his wife's sister in zika, as I have written. And so too here, even though initially each one could have performed yibbum with her, nevertheless, if afterwards the one who has children died, the first becomes forbidden to the third, for she appears as the one bound by zika to this deceased brother, and behold, his wife is forbidden to him under the penalty of karet since he has children, and automatically this one also becomes forbidden, for her rival wife is like her.

Nevertheless, this law is perplexing to me. Aside from the fact that it does not accord with all the opinions we have explained, as is understood, it is difficult for me to see how this is comparable to the previous law. For there, this co-wife appears like the co-wife of his wife's sister, since the wife of this one is also subject to the matter of yibum, except that she is a forbidden relation and this co-wife is like her co-wife, as has been written. But this one who has children, his wife is not included in the category of one subject to yibum at all, for zika is only called such when he did not leave children, as this is the essence of the passage of yibum. But regarding one who has children, what connection does he have to the matter of yibum? And if so, in what way does she appear as one subject to his zika? And the Talmud and the poskim would not have omitted mentioning such a common law—that if one died without children and has brothers, and in the meantime another brother who has children died, that the first woman should be forbidden to the remaining brothers. It requires further study.

It has already been explained in siman 172 regarding the laws of yibum with a minor and a deaf-mute woman, whose marriages are of rabbinic status, what their law is. Now we shall explain their law regarding the matter of forbidden relations in yibum. Two brothers of sound senses married to two sisters who are minors or deaf-mutes, and one of them died, she is released because of "the sister of a wife," for the marriages of both of them are equal. If one was of sound senses and one was a deaf-mute: if the husband of the deaf-mute died, she is released because of "the sister of a wife." If the husband of the one of sound senses died, he must send away his wife with a get, for her marriage is of rabbinic status and she became forbidden to him because of the sister of his wife who fell before him for yibum according to the Torah; and his brother's wife he sends away with chalitzah, and it is forbidden to perform yibum with her by rabbinic decree because she is, in any event, the sister of his wife by rabbinic decree.

If one was an adult and one was a minor: if the husband of the minor died, she is exempt because of "a wife's sister." If the husband of the adult died, we instruct the minor to perform mian against her husband, and he performs yibum with the adult. Regarding a deaf-mute woman, this remedy is impossible, but regarding a minor where mian is possible, even though one should distance oneself from mian, nevertheless, in order to fulfill the mitzvah of yibum, we instruct her to perform mian. And if she did not perform mian and grew up with him, even if he had relations with her after she grew up, we compel him to divorce her, for she was forbidden to him during her minority since we maintain "there is zika," and so they ruled in the Gemara (110a, the halakha is like Rabbi Eliezer, see there). And some say that in the Gemara they only ruled this initially, but post facto, when she grew up and he had relations with her, the zika was nullified and she is permitted to remain with him (Bach). But they did not agree with his words, for even post facto, since the mitzvah of yibum fell upon him, the yevama is not exempted by the fact that her minor sister grew up with him (Beit Shmuel, subsection 10, for it is Rabban Gamaliel who maintains on 109a: one who betrothes the sister of a yevama, the yevama is exempted, and we do not maintain accordingly, see there).

Two brothers, one of sound senses and one a cheresh, married to two sisters who are of sound senses, or one a cheresh and one of sound senses, and the woman of sound senses is married to the man of sound senses: if the cheresh who was the husband of the cheresh died, or the cheresh who was the husband of the woman of sound senses died, she is exempt because of being the sister of a wife. If the man of sound senses who was the husband of the woman of sound senses died, and her zikah to his brother is from the Torah, while the marriage of a cheresh is rabbinic—whether his wife is of sound senses or his wife is a cheresh—therefore the cheresh must send forth his wife with a get, for just as her entry into marriage was through gestures, so too is her exit. But for the wife of the man of sound senses there is no remedy, and she is forbidden forever, for the cheresh is not fit to perform chalitzah, and to perform yibbum is forbidden rabbinically, for rabbinically she is an ervah to him as the sister of his wife. And the divorce does not avail, because at the time of her falling for yibbum she became forbidden to him rabbinically.

Two deaf-mute brothers married to two sisters who are hearing, or deaf-mutes, or one deaf-mute and one hearing; and similarly, two deaf-mute sisters married to two brothers who are hearing, or deaf-mutes, or one deaf-mute and one hearing; and one of them died—she shall go out because of "a wife's sister," for their marriages are of equal status. Therefore, if they were strangers to one another, they may perform yibbum, and if they afterwards desire to divorce with a get, they may divorce. All of this was explained in siman 172; see there.

Two brothers, one of sound senses and one a cheresh, and the cheresh is married to two women of sound senses, and one of them is an ervah to the one of sound senses—for example, she is his wife's sister or the like—both are exempt from chalitzah and from yibbum, for his marriage is rabbinic and his zikah is rabbinic. And if both were of sound senses, and one of them was married to two women, one of sound senses and one a cheresh, and the cheresh is an ervah to his second brother; when this one who has the two women dies, the one of sound senses is cast before his brother for yibbum, and she is not like the rival-wife of an ervah, for the marriage of the cheresh is rabbinic, and only by rabbinic law is she the rival-wife of an ervah. Therefore, the one of sound senses performs chalitzah and does not undergo yibbum (Tosefta, chapter 9). And the Rambam wrote at the end of chapter 7: Everywhere we have said "two sisters," it means either two sisters, or a woman and her daughter, or a woman and her daughter's daughter, and the like; and the matter is that they are two women where one of them is an ervah with the other and it is impossible to marry both of them because of ervah. Thus far his words. And it is necessary to know that in one matter a wife's sister is different from all other arayot: for all other arayot are forbidden forever even if the ervah died, whereas a wife's sister is only forbidden during her lifetime, even when she was divorced, but not when she died prior to her falling for yibbum.