I would say that the levirate bond applies as long as the yevama requiring levirate marriage is alive but that after her death the bond was terminated. In other words, after the yevama died any relationship between the two dissolved. This comes to teach us that the bond is not terminated without cause but instead requires an actual act, such as ḥalitza or levirate marriage. Until one of these acts is performed, the bond remains in place. Let us say that it supports Rav Yehuda’s opinion from that which was taught: If his yevama dies, he is permitted to marry her sister. From here the Gemara deduces: Her sister, yes; her mother, no, in accordance with the opinion of Rav Yehuda.

The Gemara rejects this: The same is true, that even her mother is permitted. And this language was used only since he taught in the first clause of the baraita: If his wife dies he is permitted to take her sister; specifically her sister but not her mother, as she is forbidden by Torah law. Therefore, he also taught in the latter clause that he is permitted to marry her sister.

Rav Huna bar Ḥiyya raised an objection to this from the mishna: If he performed levirate betrothal with her and then died, the second woman performs ḥalitza and may not enter into levirate marriage. This implies that the reason is specifically that he performed levirate betrothal with her. Had the brother not performed levirate betrothal with her, the second woman would also be permitted to enter into levirate marriage. And if you say that the levirate bond is substantial, then she would be considered a rival wife of the wife of a brother with whom the third brother did not coexist by that bond. Since the wife of a brother with whom he did not coexist is prohibited from entering into levirate marriage, her rival wife would likewise be forbidden from doing so.

Rabba said: This should not be read precisely, as the same is true even if the second brother did not perform levirate betrothal; the second woman must perform ḥalitza but may not enter into levirate marriage, as the levirate bond renders her a rival wife of the wife of a brother with whom the third brother did not coexist.

And the reason that it teaches the case of levirate betrothal specifically was in order to exclude the opinion of Beit Shammai, who said: The legal status of levirate betrothal with a yevama eligible for levirate marriage is that of a full-fledged acquisition, and it is legally binding to the same degree as an actual betrothal. Therefore, even ḥalitza would be unnecessary, similar to the case of a rival wife of a forbidden relation. This is what it comes to teach us: Even if he performed levirate betrothal she is not truly considered the rival wife of a forbidden relation; the prohibition concerning her is by rabbinic law, and she is therefore required to perform ḥalitza.

Abaye raised an objection to this from that which was taught: In the case of two brothers who coexisted, and one died childless and the second arose to perform levirate betrothal with his yevama but did not manage to perform levirate betrothal before a third brother was born, and then the second brother, who also had a wife, died, whereby both women would fall before the newly born brother for levirate marriage, then the first goes out and is not obligated in levirate marriage because she is the wife of his brother with whom he did not coexist, and the second woman, who was the wife of the second brother, either performs ḥalitza or enters into levirate marriage. But if you say that the levirate bond is substantial, then the wife of the second brother would be rendered a rival wife of the wife of a brother with whom he did not coexist by that bond.

The Gemara rejects that: In accordance with whose opinion is this? It is the opinion of Rabbi Meir, who said: The levirate bond is not substantial. The Gemara asks: Does Rabbi Meir hold that the levirate bond is not substantial? After all, unattributed mishnayot are in accordance with the opinion of Rabbi Meir, and didn’t we learn in a mishna (26a): In the case of four brothers, two of whom are married to two sisters, if those married to the sisters died, whereby both sisters fall before the surviving brothers for levirate marriage, then those two sisters must perform ḥalitza and may not enter into levirate marriage. It would seem that the reason for this is that each of the sisters has a levirate bond to both remaining brothers.

And if it enters your mind to say that Rabbi Meir held that the levirate bond is not substantial, didn’t these two sisters come from two different houses, as each was married to a different brother? If so, one brother should take one in levirate marriage and the other should take one in levirate marriage.

The Gemara answers: Actually, in Rabbi Meir’s opinion the levirate bond is not substantial. The mishna states that they perform ḥalitza and do not enter into levirate marriage because he held that it is prohibited to nullify the mitzva of levirate marriage. That is to say, it is prohibited to act in such a way that the mitzva of levirate marriage becomes obviated. Under these circumstances there is concern that perhaps as one brother performs levirate marriage to one of the sisters the other brother dies before he manages to perform levirate marriage to the other. If that were to happen, you would thereby nullify the mitzva of levirate marriage since the sister that would now fall before the remaining brother would be his wife’s sister and therefore prohibited from entering into levirate marriage with him.

The Gemara objects: But if the levirate bond is not substantial, then let the mitzva of levirate marriage be nullified. That is, if the levirate bond does not carry any real obligation, then the mitzva itself never truly came into effect. As Rabban Gamliel said: The levirate bond is not substantial, and it is permitted to nullify the mitzva of levirate marriage.

As we learned in a mishna (109a): That mishna discusses a case of two brothers who were married to two sisters. One sister is an adult and therefore her marriage was fully effectual, and one sister is still a minor, and she was orphaned from her father, and her marriage was valid only by rabbinic ordinance. If the brother who was married to the elder sister died, then that sister falls for levirate marriage before the brother married to the minor. Under these circumstances, the Sages suggested directing the minor to refuse her marriage to her husband so that he would be able to take his brother’s wife in levirate marriage. If the minor does not do so, he would be unable to take her sister in marriage, as she would be the sister of his minor wife and thereby fully exempt from the levirate obligation. Rabban Gamliel said: If the minor refused in the meantime of her own accord, then she refused, but if she did not refuse, let her wait until she reaches the age of maturity, and then that other adult sister will be exempt from performing ḥalitza or levirate marriage due to the fact that she is his wife’s sister. Here it is apparent that Rabban Gamliel is not concerned about nullifying the mitzva of levirate marriage from one of them.

Rabba said to Abaye: Do you wish to raise a contradiction between the words of Rabban Gamliel and Rabbi Meir? This would imply that the contradiction needs to be resolved, but statements from two different tanna’im do not need to agree or to be resolved. Abaye responded: No, in fact this is what we meant to say: How could one possibly say that Rabbi Meir is concerned lest there be nullification of the mitzva of levirate marriage even when it is uncertain because perhaps the first brother will not die, whereas Rabban Gamliel is not concerned that the mitzva be nullified even when it is certain? It is surprising that there should be such a great difference between the tannaitic opinions. Rabba answered: Perhaps the one who is not concerned about nullification of the mitzva of levirate marriage is not concerned even if nullification is certain, and the one who is concerned is concerned even if nullification is uncertain.

With regard to the actual dispute between Rav Huna and Rav Yehuda, Abaye said to Rav Yosef: This halakha stated by Rav Yehuda, that even if a woman waiting for levirate marriage dies her mother is still forbidden to the yavam, is from his teacher Shmuel and not from Rav, who was also one of his teachers. Evidence for this can be found in that which we learned in a mishna (41a):