Explanation: It is unreasonable that the majority of a complete [fetus] that came out backwards, or the majority that came out normally [head first] and cut up, R. Yosi would not consider it to be born;

Rav Papa said that the text of the Beraisa says "cut up and backwards."

Inference: If it were cut up and came out normally, the head exempts, and R. Yosi holds that the head does not exempt;

This is [just like] the argument of R. Yochanan and R. Elazar.

Implied question: Perhaps R. Yosi comes to say that even normally (head first), we require the majority, and the head does not exempt, and the same applies if it came out backwards, the majority suffices!

Answer: If so, R. Yosi should have said "even if it came out normally, [it is not born] until the majority leaves. This would imply that he comes to be stringent;

Therefore, Rav Zevid answers that since he said "once it came out normally", and he did not say "until it comes out", this connotes that R. Yosi comes to be lenient;

He says as follows. If it came out cut up and backwards, [it is not born] until the majority leaves. This implies that if it came out normally, the head exempts;

R. Yosi is lenient, and says "when it comes out normally l'Chayim."

Explanation #1: "L'Chayim" is what is considered life, i.e. the majority of the head, like the Beraisa below explains - R. Yosi says, from when the majority of the head comes out.

Explanation #2 (R. Chananel): "L'Chayim" means a viable baby. The head exempts only for a viable baby, but not for a Nefel.

Question: If so, why was Shmuel refuted in Bechoros (47b)? R. Yosi holds like him!

Implied question: This is a Sefek-Sefeka. Why must she observe [two weeks of Tum'ah like Yoledes] Nekevah? (Perhaps there was no child. And even if there was, perhaps it was a male!)

Answer: If you would be Metaher her from Tum'as Nekevah due to a Sefek-Sefeka, you will also be Metaher her [from seven days of Tum'as Nidah] if she will see [blood] on days 34 and 41, due to Sefek-Sefeka. (Perhaps she did not give birth at all. Day 34 began Nidah, and on day 41 she is only Shomeres Yom k'Neged Yom. And even if there was a child, perhaps it was a female, and both sightings were Dam Tohar.)

You will not be concerned lest she gave birth to a male (due to the Sefek-Sefeka). These two leniencies contradict each other, like we explained above (27a)!

Distinction: However, regarding To'eh (29b, one who is unsure whether she miscarried, and when this occurred) we are stringent even though there are several Sefekos. (Tosfos ha'Rosh says that there is different, for she already was Teme'ah. I.e. here, perhaps there was no miscarriage and she is Tehorah. She will be Nidah the next time she sees (Rashi).)

Explanation: The case is, the animal did not delay outside. If it delayed, perhaps it gave birth and excreted Tinuf (fluids)!

Question: Why didn't R. Yosi b'Ribi Chanina think of this answer? There is no other way to explain the Beraisa! (Ran - most women immediately sense that they miscarried. R. Yosi reasoned, if we do not rely on this majority (rather, we are concerned lest she gave birth many days ago), we should not rely on the majority that most women give birth to a proper child, either. Ravin says that we rely on the latter majority, but not on the former.)

Question #1: All the more so this is like Rabanan, who forbid below (67b) Bi'ah mid'Oraisa!

Question #2: Here it connotes that R. Shimon does not forbid Tevilah; he forbids only Bi'ah. Below (67b) it connotes that he forbids Tevilah!

Answer: The Amora'im forbade Tevilah. Below (67b DH Aval) we will explain with Hash-m's help. (There, the Maharsha says that our Tosfos relied on what he wrote below, that we could explain that Rabanan permit even Bi'ah. Therefore, also Question #1 is resolved.)

Question: Since she saw [blood] from the start of the night, why do Beis Shamai say that she immerses at night, due to Tevulas Yom Aruch? (I.e. perhaps today ended Dam Tohar, and now she immerses to permit her to Terumah. If she saw immediately at night, the Tevilah does not help!)

Answer: It is not precise that she saw immediately at night, rather, an hour or half hour into the night. She immersed at the beginning of the night, and sees right after immersing;

If she wants to have Bi'ah before immersing, she may. (The Tevilah is only for the sake of Terumah.)

Observation: This elaboration is only for the sake of [explaining] Beis Hillel. According to Beis Shamai, she immerses all 80 nights due to Tevulas Yom Aruch. (Perhaps Yemei Tohar just ended.)

Observation: The first week of nights is unlike the two weeks during the day. Rather, it is six nights during the first week and the first night of the second week;

Also the second week of nights is six nights during the second week and the first night of the third week;

The second and third weeks during the day are not like this.