Answer: One might have thought that regarding a woman permitted by Beis Din, this is like rumors that started before Nisu'in (since there was doubt from the beginning, and she should be forbidden). He teaches that this is not so.

(Mishnah): If she was married according to Beis Din (... she is exempt from a Korban).

(Ze'iri): Based on what was taught in the Beis Medrash, the Halachah does not follow the Mishnah.

(Beis Medrash): If Beis Din ruled that the sun set, and later it shone, this was a mistake, not a Hora'ah (ruling. Similarly, our Mishnah is a mistake, and not a Hora'ah).

(Rav Nachman): The case of our Mishnah is a Hora'ah.

Support (Rav Nachman, for himself): In all of Torah, one witness is not believed, but here, he is believed. This is because it is a Hora'ah!

(Rava): It must be a mistake!

If Beis Din permitted Chelev and blood, and later forbade them, if they again permit them (without a solid reason), we do not listen to them!

Here, if we permitted her to remarry based on one witness, and then forbade her according to two witnesses, and then a witness came [and said that her husband subsequently died], we permit her!

Surely, it is because it was a mistake!

Support (Beraisa - R. Eliezer): The law pierces the mountain, and she brings a fat Chatas.

Question: If it was a mistake, we understand why she brings a Korban. However, if it was a Hora'ah, why does she bring a Korban?

Suggestion: Perhaps R. Eliezer obligates an individual who acted according to a (mistaken) Hora'ah of Beis Din to bring a Korban!

Rejection: If so, why did he say 'the law pierces the mountain'?! (This suggests that one might have thought differently. According to this suggestion, obviously she brings a Korban!)

(Mishnah): If Beis Din ruled that she may remarry (and she was Mekalkel, she brings a Korban).

Question: What does 'Kilkelah' mean?

Answer #1 (R. Elazar): She had Bi'as Zenus.

Answer #2 (R. Yochanan): She married someone she is forbidden to, e.g. a widow married a Kohen Gadol, or a divorcee or Chalutzah married a regular Kohen.

R. Elazar says that she brings a Korban for Bi'as Zenus, all the more so she brings for a forbidden marriage;

R. Yochanan exempts for Bi'as Zenus. She tells Beis Din 'you told me that I am single!'

Support (for R. Yochanan - Beraisa - R. Elazar): If Beis Din ruled that she may remarry and she was Mekalkel, e.g. she married a Kohen Gadol, or she was a divorcee or Chalutzah and she married a regular Kohen, she must bring a Korban for every act of Bi'ah;

Chachamim say, she only brings one Korban.

Chachamim agree that if she married five men she must bring a Korban for each one, since they are separate bodies.

(Mishnah): A woman's husband and their only son went overseas. They told her that her husband died and then her son died. She remarried. Later, they told her that her son died first (so she was Zekukah l'Yibum). She must leave her husband. Her children from him, both the first and last, are Mamzerim.

If they told her (the first time) that her son died and then her husband, and she did Yibum, and later they told her that her husband died first, she must leave the Yavam. Her children from him, both the first and last, are Mamzerim;

Witnesses told a woman that her husband died, and she remarried. Later they told her that he was alive when she remarried, but later he died. She must leave her husband, and her first children from him are Mamzerim. Later children are not Mamzerim;

If witnesses told her that her husband died, and she became Mekudeshes, and later, her husband returned, she may return to him. Even if the second husband divorces her, she is permitted to Kehunah;

R. Elazar ben Masya says "A woman divorced from her husband (is forbidden to a Kohen)", but not a woman divorced from a man who is not her husband.

(Gemara) Question: What does 'the first and last children' mean?

Suggestion: First children are those before the latter report. Last are those after the latter report.

Objection: If so, the Mishnah should simply say that her children are Mamzerim!

Answer and defence of Suggestion: Indeed, it could have. Since the Seifa (c) distinguishes between the first and last children, also the Reisha mentions them.

(Beraisa): This Mishnah is R. Akiva, who says that Ein Kidushin Tofsin b'Chayavei Lavin. Chachamim say that a Mamzer does not result from a Yevamah who married a stranger (anyone other than her Yavam).

Question: Why didn't it cite Chachamim to say that a Mamzer does not result from Chayavei Lavin?

Answer: These Chachamim hold like R. Akiva according to a different Tana, who says that a Mamzer results from Chayavei Lavin only if they are of She'er (kin).

(Rav): "Lo SiHYeH Eshes ha'Mes Chutzah l'Ish Zar" - HavaYaH (Kidushin) does not take effect between a Yevamah and a foreign man.

(Shmuel): Due to our ignorance, (if someone else was Mekadesh her) she needs a Get (to marry anyone else).

Shmuel is unsure whether "Lo Sihyeh" teaches (R. Tam - only) that this is a Lav, or (also) that Ein Kidushin Tofsin.

(Ameimar): The Halachah follows Shmuel.

(Rav Ashi): According to this, if her Yavam is a Kohen and she married Levi (a stranger), they do Chalitzah, and she is permitted to Levi.

Objection: We should not allow him to profit from his sin!

Correction: Rather, if her Yavam is a Yisrael, Levi gives her a Get, and she is permitted to her Yavam.

(Rav): Ein Kidushin Tofsin with a Yevamah. Nisu'in takes effect.

Question: If Kidushin does not take effect, neither does Nisu'in!

Answer #1: Rather, she has neither Kidushin nor Nisu'in.

Answer #2: 'She has Nisu'in' like Rav Hamnuna taught:

(Rav Hamnuna): If a Shomeres Yavam had Bi'as Zenus she is forbidden to her Yavam.

Answer #3: Nisu'in takes effect to require a Get. This is a decree lest she be confused with a woman who remarried based on one (false) witness.

(R. Yanai): They voted and concluded that Ein Kidushin Tofsin with a Yevamah.

Question (R. Yochanan): A Mishnah teaches this!

(Mishnah): If David was Mekadesh a woman to take effect (when it will be possible, i.e.) after he or she converts or is freed, or after her husband dies, or after her sister (David's wife) dies, or after she will do Chalitzah, she is not Mekudeshes (even afterwards. If Kidushin Tofsin b'Yevamah, it would take effect.)

Answer (R. Yanai): Correct! Had I not taught to you the law, you would not have seen that the Mishnah teaches it!

(Reish Lakish to R. Yochanan): A great man praised you. If not, I would have said that the Mishnah is like R. Akiva, who says that Ein Kidushin Tofsin with Chayavei Lavin (but Chachamim say that Kidushin Tofsin b'Yevamah)!