Abaye and Rava conducted according to Rabah and Rav Yosef. Rav Ashi acted like the opinion of Rav and Shmuel, and was stringent (to put Mezuzos on both openings, like R. Yosi).

The Halachah follows Rav and Shmuel, (and) we are stringent.

(Rav Huna): If there is an opening in the ceiling to the attic, if there is only one doorway (at the top or bottom of the staircase leading to it), it requires a Mezuzah. If there are two, both require Mezuzos.

Inference (Rav Papa): This teaches that if a room is open to porches on all four sides, all require Mezuzos.

Objection: This is obvious!

Answer: The Chidush is, even though he normally uses one of them more than the others (since when he made them, all were needed).

(Ameimar): A corner opening (neither of the walls reaches to the corner, like this __ ׀) requires a Mezuzah.

Question (Rav Ashi): it has no doorposts!

Answer (Ameimar): The ends of the walls are its doorposts (even though the gap between them is not in line with either wall, rather, on a diagonal).

Rav Mari visited Shmuel. He saw a Mezuzah on an opening with only a left doorpost.

Rav Mari: Do you hold like R. Meir (who requires a Mezuzah when there is only one doorpost? He says this only when it is on the right, but not when it is on the left!

(Beraisa) Suggestion: Perhaps one should put the Mezuzah on the left side!

Rejection: We read "Beisecha" as if it says 'Bi'asecha'. It must be on your right side when you enter.

Question: How do we learn this from the verse?

Answer (Rabah): 'Bi'asecha' is the way you enter, i.e. on the right;

(Most) people move their right foot first when they begin walking.

(Rav Shmuel bar Acha): "(A chest was put)... Etzel ha'Mizbe'ach mi'Yamin b'Vo Ish Beis Hash-m" (people enter the Mikdash from the east. The chest was on the right, on the side that people enter.)

Question: Where do we find that R. Meir requires a Mezuzah when there is only one doorpost?

Answer (Beraisa - R. Meir): A Mezuzah is required even if there is only one doorpost;

Chachamim exempt.

Question: What is Chachamim's reason?

Answer: It says "Mezuzos". (The plural teaches that there must be two doorposts.)

Question: What is R. Meir's reason?

Answer (Beraisa - R. Yishmael): "Mezuzos" teaches that there must be two doorposts;

Question: Why does it repeat "Mezuzos" (plural) in the second Parshah?

Answer: This is a Ribuy followed by another Ribuy. This always comes to exclude;

We exclude (the need for) one of the two doorposts.

R. Akiva: We need not expound that way! It says (to put the blood of Korban Pesach in Mitzrayim) "... v'Al Shtei ha'Mezuzos";

Question: Why must it say "Shtei"? We would have known that "Mezuzos" refers to two!

Answer: This teaches that whenever it says 'Mezuzos' without specifying two, it refers to one.

(Beraisa) Suggestion: Perhaps "u'Chsavtam" teaches that the Parshiyos should be written on the actual stones (of the doorpost)!

Rejection: It says here 'Kesivah', like it says about a Get (Rashi; Tosfos - Megilas Sotah, or the extra Sefer Torah that a king writes);

Just like there he writes in a Sefer, also here.

Question: Perhaps we should say oppositely! It says here 'Kesivah', and it says there (writing the Torah on rocks in Har Eival - Devarim 27:8) 'Kesivah'. Just like there it is on rocks, also here!

Answer: Let us see which is more similar. We learn Kesivah that applies to all generations from Kesivah that applies to all generations. We do not learn Kesivah that applies to all generations from Kesivah that does not apply to all generations;

Also, it is like it says there "va'Yomer Lahem Baruch mi'Piv Yikra Elai Es ha'Devarim ha'Eleh va'Ani Kosev Al ha'Sefer ba'Deyo."

Question (Rav Acha brei d'Rava): The Torah said "Al Mezuzos" (which connotes on the doorpost itself), and you say that we learn 'Kesivah' from 'Kesivah'?!

Answer (Rav Ashi): It is written "u'Chsavtam" - Kesivah Tamah (i.e. in a Sefer), and then [we affix it] on the doorpost.

Question: Since it is written "u'Chsavtam", why do we need a Gezeirah Shavah [to teach that we do not write on the rocks?

Answer: If not for the Gezeirah Shavah, one might have thought that we write on a rock and then fix it in the doorpost. [The Gezeirah Shavah] teaches that this is not so.

(Mishnah): The four Parshiyos in Tefilin are Me'akev each other. Even one Kesav (letter) is Me'akev.

Objection: This is obvious! (We learn from Mezuzah. There it says "u'ChsavTam" - the Kesav must be Tam (complete).)

Answer #1 (Rav Yehudah): The Mishnah teaches that even the Kotz (protrusion) of a 'Yud' is Me'akev.

Objection: Also this is obvious! (If it is missing, the letter is invalid.)

Answer #2 (Rav Yehudah): The Mishnah teaches that if a letter is not surrounded by blank parchment on all four sides, it is Pasul.

(Beraisa - R. Yishmael): Two occurrences of 'Totafos' are written missing the 'Vov' (as if it says 'Totafas', singular). We only learn one from each of those, and two from "Totafos" written with a 'Vov', making four in all. This teaches that there are four compartments in the head Tefilin;

R. Akiva says, we need not expound this way. In Katfi (a place), 'Tot' means two. In Afriki, "Fos' means two.

(Beraisa) Suggestion: Perhaps the four Parshiyos should be written on four parchments, and each is put in its own Bayis (box) made from a separate piece of hide!

Rejection: "Ul'Zikaron Bein Einecha" - it should be only one commemoration;

To fulfill both verses, the four Parshiyos are written on separate parchments, each is put in its own Bayis, and all four Batim are made from one piece of hide;

If the Parshiyos were written on one parchment and (the Klaf was folded like an accordion, so) each Parshah was in its own Bayis, this is Kosher.

Rebbi says, there must be a space between the Parshiyos (Rashi; Rosh - between the Batim);

Chachamim say, there need not be.

All agree that a string must separate the Batim (some say, only if the Parshiyos are on one parchment). If the separation between Batim is not recognizable (from the outside), it is Pasul.

(Beraisa): The Parshiyos for the Shel Yad (the hand Tefilah) are written on one parchment;

If they were written on separate parchments and put in one Bayis, this is Kosher;

R. Yehudah says, the parchment must be glued (or sewn) together - "v'Hayah Lecha l'Os Al Yadecha." Just like externally there is only one Os (i.e. Bayis), also internally (there must be only one parchment).

R. Yosi says, one need not attach the parchments.

R. Yosi: R. Yehudah agrees that if one has two head Tefilin but no Shel Yad, he wraps leather around one of them (so it will appear like one Bayis) and ties it on his arm.

Objection: R. Yehudah argues precisely in this case. He says that there must be only one parchment inside!

Answer (Rava): From R. Yosi's words we learn that R. Yehudah retracted.

Question: R. Chananyah said in the name of R. Yochanan that the Shel Yad may be used for the head, but not vice-versa, because we ascend in Kedushah, but we do not descend! (If R. Yehudah retracted, this is not like either Tana.)

Answer: R. Yosi permits using a Tefilah prepared (but not yet used) for the head for the hand (this is not considered descending in Kedushah), but not if it was worn on the head.

According to the opinion that preparation has significance, we must say that he stipulated from the beginning that he may use it for the hand.

(Beraisa #1): The order of the Parshiyos, from the right, is "Kadesh Li" and "Ki Yevi'acha." "Shma" and "v'Hayah Im Shamo'a" are on the left. (Rashi - Shma is next to Ki Yevi'acha; R. Tam - Shma is on the far left.)

Contradiction: Another Beraisa (#2) gives the opposite order!

Answer (Abaye): Beraisa #1 gives the order (from right to left) from the perspective of someone facing the wearer. Beraisa #2 is with respect to the wearer (Rashi; Shimusha Raba switches these.)