Explanation #1: A Tosefta (Ohalos 9:5) teaches that if one threw a chest full of Kelim over a Mes, it is Tamei. This is Ohel Zaruk, which is not considered an Ohel [to block Tum'ah];

If it was stationary, i.e. it stands in one place, it is Tehorah. Since it does not move from its place, now it is a fixed Ohel.

Inference: Ohel Zaruk is not considered an Ohel according to R. Yosi b'Rebbi Yehudah.

Distinction: However, if they argue about [whether Chachamim decreed about] the air or the earth, it is not difficult for him at all from this Beraisa, for we can establish their argument to be about a stationary chest or box. Even so, it says [that] Rebbi is Metamei due to the air;

However, now that they argue about Ohel Zaruk, we cannot establish their argument regarding when it is stationary, for if so, Rebbi would not be Metamei, for it is a proper Ohel!

We answer that all agree that they decreed about the air, and Ohel Zaruk is not considered an Ohel according to R. Yosi b'Rebbi Yehudah;

Even so, since it is not common to enter in a chest, box or tower, they did not decree, according to R. Yosi [b'Rebbi Yehudah]. The Beraisa is b'Nichusa (a support).

Explanation #2: [The Gemara says that] no, all agree that they decreed about the earth. [R. Yosi b'Rebbi Yehudah] holds that Ohel Zaruk, i.e. he entered in a chest that an animal or person moves it, is considered an Ohel to separate and block [Tum'ah];

Observation: We must say that it is better than a Talis raised in the wind. A Mishnah (Ohalos 8:5) teaches that it does not block Tum'ah or bring Tum'ah!

Explanation: Here it is better, because the legs of the person or animal carrying the chest or box touch the ground. The Talis is floating in the air. (This is clear from the Mishnah there. It says that if rocks hold down the corners of the Talis, and the wind raised the middle, it brings Tum'ah.)

Explanation (cont.): [Rebbi] holds that Ohel Zaruk is not considered an Ohel. This is why it says veha'Tanya, b'Nichusa.

Support: Also R. Chananel explained like this. R. Yosi b'Rebbi Yehudah says that if one threw a box full of Kelim over a Mes, it is Tamei, for this is like an airborne Talis. It is totally in the air;

If it was resting on an animal or person who carries it, it is Tehorah, for an Ohel Zaruk in such a case, that the legs of those carrying it touch the ground, is considered an Ohel to block Tum'ah.

Explanation: All agree that they decreed about the air. R. Yosi b'Rebbi Yehudah is Metaher because even when they decreed about the air, this refers to one who stands on a bridge of Eretz ha'Amim, or enters in a wagon or boat, which are common to go in them;

However, it is not common to enter in a chest, box or tower, so they did not decree.

Rebbi holds that even though it is not common, they decreed. The Beraisa is b'Nichusa. One who enters Eretz ha'Amim in a chest, box or tower is Tahor. One who enters in a wagon, boat or Askarya, i.e. a large ship with a mast [he is Tamei].

[The ship is called] Askarya, for this is the mast, like we say elsewhere (Ta'anis 21a) "Ilfa hung himself from the mast of the ship."

Inference: Even R. Yosi b'Rebbi Yehudah, who is Metaher in a chest, box or tower, agrees that [one who enters] in a wagon or boat is Tamei, for they decreed about the air.

Explanation (cont.): [The Gemara says that] alternatively, [they argue about whether or not we decree] lest he stick his head or the majority of his body to there. All agree that they decreed about the earth.

R. Yosi b'Rebbi Yehudah is Metaher, because he holds that Ohel Zaruk is considered an Ohel, and he does not decree lest he stick out his head or the majority of his body;

This is because the opening of the chest, box or tower is not comfortable to enter and leave, and it is not so easy to stick out his head;

Distinction: However, in a wagon or boat he is Tamei, for they decreed lest he stick his head or majority of his body outside of the wagon or boat, and tower above the earth, for it is easy to stick his head or majority outside of a boat or wagon;

Rebbi is Metamei even in a chest, box or tower. He decrees even in these, lest he stick out his head or majority.

Explanation: This implies that in a wagon or boat he is Tamei, even if he did not stick out his head or majority, for it is easy to stick out from a wagon or boat.

Implied question: We bring from this Beraisa in Eruvin (30b) and Chagigah (25a) of one who enters Eretz ha'Amim in a chest, box or tower, that R. Yosi b'Rebbi Yehudah and Rebbi argue about whether or not an Ohel Zaruk is considered an Ohel!

Answer: This is like we wanted to say here in the first answer, that they argue about an Ohel Zaruk;

However, in these [latter] answers, regarding Eretz ha'Amim, they do not argue about Ohel Zaruk. However, they argue about it (Ohel Zaruk) regarding a Mes;

(Beraisa): If it was stationary, it is Tehorah, for Ohel Zaruk is considered an Ohel;

That is like R. Yosi b'Rebbi Yehudah. Rebbi is Metamei, for he holds that Ohel Zaruk is not considered an Ohel.

Explanation: [Since he must grow his hair,] how can we say that he is not Mevatel the previous days? B'Al Korcho, he cancels the previous days!

Rather, it is a long Nezirus, and it teaches that he begins and counts immediately. This teaches that he begins and counts after Yemei Sifro. This implies that Yemei Sifro do not count.

Citation of Gemara: [Rav Sharbiya] asked the question, and answered it. It is a Nezirus of 50 days.

Explanation: This (Nezirus of 50 days) is what our Mishnah discusses. This is the small Nezirus of Rav Chisda.

It means as follows. This is only for a small Nezirus, i.e. he needed to observe only the days of a small Nezirus when the days of his Tzara'as began;

E.g. he observed 20 days of Nezirus, and Tzara'as came on him. He shaves for his Tzara'as [after it goes away], and returns to observe 30 days of Nezirus, for [after this] he has growth of hair;

I.e. in such a case it is proper that the days of Tzara'as not count at all, and it is proper that they not cancel the previous days;

If Yemei Gamro and Yemei Sifro would count for his Nezirus seven days or 14 days, according to how many days they were, he must add to the vow, in order that there will be [30 days] growth of hair;

Our Mishnah discusses such a case. It need not be a Nezirus of precisely 50 days. The same applies to a Nezirus of 40 days, when he developed Tzara'as at the end of 10 days.

Summation: This is the general rule. "A small Nezirus" is called when he needs to count only 30 days from when Tzara'as began until the end of his Nezirus.

Distinction: However, a big Nezirus, i.e. when his Tzara'as began he needed to count still 31 or 32 days of Nezirus, and all the more so more, e.g. a Nezirus of 51 or more days, and he developed Tzara'as after 20 days...

Then, surely you cannot say that all the days of Tzara'as do not count at all. At least the number of excess days [remaining above 30] count for him!

E.g. if one vowed 53 days, and observed 20 days and developed Tzara'as [for] 14 days. Three days of Tzara'as count for him, and 11 days do not count.

He must count in addition to the 23 days, [another] 30 days, for in less than this he will not have [enough] growth of hair. This is why it says "he observes [another] 30 days of Nezirus."

Explanation: This is because he is a Safek Metzora, and he may not eat Kodshim until he becomes Tahor from his Tzara'as and brings Korbanos Metzora, for a Mechusar Kipurim may not eat Kodshim;

However, due to being a Nazir Tamei, he is not forbidden Kodshim. Even though he must bring a Korban, because the Tum'ah does not come out from his body, he is not called Mechusar Kipurim.

Support: We say so in Kerisus (10a). Only one whose Tum'ah comes out from his body is called Mechusar Kipurim.

Explanation (cont.): What is the case? He vowed Nezirus for 30 days, and on the first day occurred Safek Tum'ah (of Mes) and Safek Tum'as Tzara'as, i.e. it is a Safek if real Tzara'as broke out on him, or mere white patches [that are not among the Tamei appearances].

Now, after he totally healed, he receives Haza'ah [on day three] and repeats [on day seven] and immerses, and he is Tahor from Safek Tum'as Mes, at the end of seven days.

If he wants to shave like the law of Nazir Tamei, or like a Metzora who healed, we tell him to delay shaving until 30 days, for I can say "you are a totally Tahor Nazir. You did not become Tamei";

A Nazir Tahor may not shave within 30 days, only after bringing Korbanos at the end of 30 days, when his Nezirus is finished.

It says "Ta'ar Lo Ya'avor Al Rosho Ad Melos Yemei Nizro." At the end of 30 days he shaves. The laws of bringing his Korbanos are explicit below (60a);

He brings Tziporei Metzora - the one he slaughters and the one he sends - and Chatas ha'Of, which is brought amidst Safek, due to Safek Nazir Tamei, and Olas Behemah, due to Safek Nazir Tahor.

Implied question: He may shave only after slaughtering [all] his Korbanos!

Answer: We say (46a) that if he shaved on one of them, he was Yotzei. (Here he does so l'Chatchilah, for he cannot bring all of them, due to Safek Chulin b'Azarah.)

Explanation (cont.): He stipulates about them. He is still forbidden to eat Kodshim, for perhaps he was Muchlat, and he needs to shave another time and bring Korbanos;

It says in Parshas Metzora "v'Hinei Nirpa Nega ha'Tzara'as; v'Lakach... Shtei Tziporim... v'Shachat Es ha'Tzipor ha'Echas Al Mayim Chayim; v'Shilach Es ha'Tzipor ha'Chayah; ... v'Gilach Es Kol Se'aro... va'Yashav mi'Chutz l'Ahalo Shiv'as Yamim; v'Hayah va'Yom ha'Shevi'i Yegalach... v'Rachatz Besaro ba'Mayim";

"Uva'Yom ha'Shemini Yikach Shenei Kevasim" - one is for the Olah, and one is for the Asham; "v'Kavsah Achas" is for the Chatas.

Observation: He cannot shave [the second time] at the end of seven days after the first shaving, for perhaps he was not a Metzora, but he was a Nazir Tamei, and he must begin the days of his Nezirus, the 30 days that he vowed to be a Nazir;

The 30 days that he counted do not count towards Nezirus, for we apply to him "veha'Yamim ha'Rishonim Yiplu."

Since we are unsure if he was a Nazir Tamei, and the second 30 days are Nezirus Taharah, and we apply to him "Ta'ar Lo Ya'avor Al Rosho Ad Melos Yemei Nizro", at the end of 60 days he shaves.

Explanation (cont.): In this second shaving, there is no Safek of Nazir Tamei. He fulfilled the Safek of Nazir Tamei through the first shaving at the end of the first 30 days;

However, we have a Safek whether he is a Nazir Tahor, or if this is the Tiglachas at the end of Yemei Sifro of a Metzora. He brings Olas Behemah due to Safek Nazir Tahor, in order to shave on the blood [of one of his Korbanos], and stipulates about it;

On the day after shaving, he brings Korbanos Metzora, to permit himself to eat Kodshim. He brings Chatas ha'Of, for one may not bring Chatas Behemah amidst Safek;

Rather, he makes his property Hefker, and brings Chatas ha'Of, like the law of Metzora Oni.

He brings also his Asham according to R. Shimon, who says that he can stipulate about the Asham, that [if he is not obligated to bring Asham] it is a Shelamim. Rabanan of R. Shimon hold that the Asham is not Me'akev eating Kodshim.

Explanation (cont.): He is still forbidden to drink wine and become Tamei Mes, for perhaps he was a Muchlat, and the two shavings he did were for being a Metzora, for [the end of Yemei] Gamro and [Yemei] Sifro, and they do not count for Tiglachas Nazir Tahor, like we say below (60a);

Therefore, he needs another two shavings, one for Nazir Tamei, and one for Nazir Tahor.

Explanation (cont.): At the end of 90 days [from the beginning], he shaves the third time. In this third shaving, there is no Safek of Metzora at all, only Nazir Tahor or Nazir Tamei. He cannot shave until 30 days [after the previous shaving, lest he is a Nazir Tahor], therefore it is on day 90.

Not only for a small Nezirus, he must wait 30 days due to growing hair, even according to Rav Chisda [who says that days of a Metzora count towards a long Nezirus - 55a]...

Rather, it is even for a long Nezirus, like the Gemara proceeds to explain, because [the Tana] holds that days of a Metzora do not count for him at all, unlike Rav Chisda;

Therefore, he must wait to do the third shaving after the second shaving like the number of days of Nezirus that he vowed, for perhaps he was a Nazir Metzora, and not a Nazir Tamei.

Explanation (cont.): At the end of 90 days, when he shaves the third time, there is no Safek of Metzora at all, only Nazir Tahor or Nazir Tamei. He brings Olas Behemah due to Safek Nazir Tahor, and in order to shave after blood of a Korban. He brings also Chatas ha'Of, due to Safek Nazir Tamei.

He is still forbidden to drink wine and become Tamei Mes, for perhaps he was a Muchlat, and a Nazir Tamei, and the two first shavings were for his Tzara'as, and the third was for Nazir Tamei;

Therefore, he must wait another 30 days for Nezirus Taharah. At the end of 30 days he shaves and brings Korban Taharah alone, and stipulates, like it explains below;

[Now] he may drink wine and become Tamei Mes. This is why it says "he drinks wine and becomes Tamei Mes after 120 days.

Inference (Maharam): You are forced to say that he shaves on day 30. If he did not shave until day 31, like a regular Nazir, if so he would shave the second time on day 61;

If so, he would not eat Kodshim until day 62, for after Tiglachas Metzora he immerses, and he cannot bring his Korbanos until the next day, like we said above (44b), that if he shaved on day eight, he brings Korbanos on day nine!

Note: Rather, the second shaving is on day 60. The Mishnah (59b) says that he may eat Kodshim after 60 days, i.e. on day 61.

Rather, he shaves on day 30, and brings one of the three Korbanos of a Nazir Tahor, an Olah or Shelamim, in order to shave on blood [of a Korban], for perhaps he was a Nazir Tahor.

Implied question: Other Nezirim do not shave until day 31!

Answer #1: That is mid'Rabanan. Mid'Oraisa, he may shave on day 30, according to Rav Masne because Miktzas ha'Yom k'Kulo, or according to Bar Pada because Nezirus finished on day 29;

Therefore, this Nazir, who still may not drink wine or become Tamei Mes, Chachamim did not enforce their words, and establish him on Torah law, and permit him to shave on day 30.

Objection: The third shaving is difficult. He does not drink wine [afterwards], and even so, he shaves on day 31 [from the second shaving]!

Note: Tosfos did not ask about the second shaving. In the comment below, Tosfos explains that after the first shaving, he starts counting [the next Safek Nezirus Taharah] on day 31. This is unlike Tosfos on 56a (DH Ochel), who says that he starts counting on day 30. Both hold that the second shaving is on day 30 of his count, but the third shaving is on day 31 of his count.

Answer #2: Rather, due to eating Kodshim they were lenient about the first two shavings, to do them l'Chatchilah on day 30. This is from R. Peretz.

Note: R. Simchah of Desvi says that the following comment belongs on 56a, after DH Ochel. (It argues with what Tosfos brings there from R. Peretz.)

Comment: Still, he may not bring Korbanos Nazir Tamei that day, since he must immerse after shaving, like the law of a Metzora who immerses after every Tiglachas;

It looks like Tevilas Nazir Tamei on day seven, since we also have a Safek that he is a Nazir Tamei, and then he may not bring [his Korbanos] until day eight. Therefore, he cannot bring Korbanos Nazir Tamei until the day after he shaved, i.e. day 31.

On day 31 he brings Chatas ha'Of, like the law of Nazir Tamei, for perhaps he was Tamei and not a Muchlat;

He counts another 30 days from day 31, on which he brings Korban Tum'ah, like Rabanan above (18b), who say that if he brought his Chatas, even if he did not bring his Asham, he counts [Nezirus Taharah from now].

Explanation: On day 60, which is day 30 of his count, he shaves, like I explained [above that we let him shave on day 30, to hasten his Heter to eat Kodshim].

On the next day, i.e. day 61, he brings his Korban Tzara'as, i.e. Chatas ha'Of, like a poor Metzora. If he was rich, he is Mafkir his property. He may eat Kodshim, because the Asham is not Me'akev eating Kodshim according to Rabanan;

According to R. Shimon, who says that we may [offer Kodshim in a way that might] cause Kodshim to be wasted, he brings also Asham, and stipulates about Shelamim. (If he was not a Metzora, it is a Shelamim. Chachamim forbid, for the Torah permits everyone to eat Shelamim for two days and a night, but now that it is a Safek Asham, only male Kohanim may eat it, and only for one day and a night. Perhaps it will become Nosar due to this!)

This explains what we taught (Zevachim 76a), that R. Shimon says, the next day he brings his Asham and Log [of oil], and says that if he was a Metzora, this is his Asham, and this is his Log [that is brought with Asham Metzora]. If not, it is Shelamim. That Asham must be slaughtered in the north, and blood must be put on the Behonos (his right ear, thumb and toe)...

Observation: The day after 60, i.e. day 61, he may eat Kodshim, for he already shaved two shavings. If he was a Metzora, he already became Tahor.

Distinction: We cannot say so about the third shaving, for he does not immerse after shaving, since he already fulfilled the Sefekos of Metzora;

We must say that surely, the last two shavings he does not shave until day 31, which [for the third shaving] is day 91, for his count began on day 61.

He brings Olas Behemah to shave on the blood. He also brings Chatas ha'Of due to Safek Nazir Tamei, for at the first and second Tiglachas, perhaps he was a Muchlat, and they did not count for his Nezirus.

Explanation (cont.): He begins his [last] count on day 91, and adds 29 days to day 91, which are 120 days, and shaves on day 121, which is day 31 of his count.

He brings Korban Taharah alone, and on day 121 he is permitted to drink wine, and he finishes his Nezirus.

We can explain that only for the first two shavings, which are due to Safek Metzora, they were lenient to allow [shaving] on day 30;

However, the last two shavings, during which he is not a Safek Metzora, they equated him to other Nezirim, who shave on day 31. Therefore, it says that he drinks wine and becomes Tamei Mes after 120 days.