Suggestion: Tana'im argue about the decree on Chutz la'Aretz:

(Beraisa - Rebbi): One who enters Chutz la'Aretz in a box becomes Tamei;

R. Yosi b'Rebbi Yehudah says, he remains Tahor.

Suggestion: R. Yosi holds that they decreed on the soil, and Rebbi holds that they decreed on the air.

Rejection #1: No, all agree that they decreed on the soil;

R. Yosi holds that an Ohel that is Zaruk (moving) is considered an Ohel (the bottom of the box shields from Tum'as Ohel of the soil), and Rebbi disagrees.

Version #1 (in Tosfos) Objection (Beraisa - R. Yosi): If a box full of Kelim was thrown over a Mes, the Kelim become Tamei. If the box was stationary, the Kelim remain Tahor. (This shows that he agrees that an Ohel Zaruk is not an Ohel!)

Version #2 - Support (Beraisa - R. Yosi): If a box full of Kelim was thrown over a Mes, the Kelim become Tamei. If the box was (carried by people or animals) on the ground, the Kelim remain Tahor. (This shows that he holds that an Ohel Zaruk is an Ohel.) (end of Version #2)

Rejection #2: Both hold that the decree was on the air;

R. Yosi holds that Chachamim did not decree about entering Chutz la'Aretz in a box, since this is uncommon. Rebbi holds that they decreed even in such a case.

Support (Beraisa): If one enters Chutz la'Aretz in a box, he is Tahor. If he enters in a wagon, boat or large ship with a mast, he is Tamei. (This is like R. Yosi.)

Rejection #3: They argue about whether or not we decree lest he stick his head or the majority of his body outside the box.

Support (Beraisa - R. Yosi): If one enters Chutz la'Aretz in a box he is Tahor until he sticks out his head or the majority of his body.

(Mishnah): He (re-)starts counting...

(Rav Chisda): This applies only to a small Nezirus. Regarding a long Nezirus, the days (of Sefirah and of Muchlat) count.

Question #1 (Rav Sharbiya - Mishnah): He begins counting immediately, and does not cancel previous days.

Question: What is the case?

Suggestion: If he was a Nazir for only 30 days, previous days are Batel, for he must grow 30 days of hair to complete Nezirus!

Answer: Rather, it was a long Nezirus. The Mishnah says that he starts counting immediately (after Taharah)!

Answer (Rav Sharbiya): Rav Chisda discusses a 'long Nezirus', i.e. when 30 days remained after the Tzara'as, e.g. a 50 day Nezirus and he became Muchlat after 20 days.

After shaving at the end of Tzara'as, he observes the 30 remaining days of Nezirus.