Explanation #1: The case is, he already has a receipt. Therefore, once he paid it, [the lender] is exempt [for Hotza'ah of the document], for he need not return the document.

Explanation #2: Rashi connotes that the receipt was not written yet.

Objection: [If so,] he must return it to the borrower, so he will not need to write a receipt!

Citation: A Tosefta in Shabbos (8:12) teaches that R. Yehudah says that even one who is Motzi a paid document of any size is liable, for he guards it [to show it] to a creditor.

Question (Rashba): This is difficult for the other Amora'im! (Why didn't the Gemara challenge them from the Tosefta? It is proven that the borrower is Motzi it!)

Implied question: He should have said "since it is destined to be woven", which is further away (more things must be done beforehand. Maharshal - in Tosfos' text, also the Shi'ur for weaving is a double Sit. This is the Yerushalmi's text - Pnei Yehoshua.)

Answer: Perhaps not all are destined to be woven.

Explanation: He holds like R. Elazar, who says that Edei Mesirah Karsei (witnesses who see a document given empower it). According to R. Meir (who holds that Edei Chasimah Karsei, witnesses who sign a document empower it), one may not write on Diftara (a hide that was salted and treated with flour, but not Afitz, i.e. treated with gallnuts);

Source: A Mishnah (Gitin 21b) says that one may not write on erased paper or Diftara. Chachamim are Machshir. The Gemara says that Chachamim are R. Elazar.

Explanation #1: Rashi explained, for no good reason, that the Shi'ur of a Get is smaller than all of them.

Rebuttal: We find that the Shi'ur for parchment is to write the smallest Parshah in Tefilin (Shma Yisrael), and paper, which is inferior, its Shi'ur is to write a tax receipt (which is only two letters)!

Explanation #2: The reason for parchment is because it is important, people do not store it for a tax receipt. We can explain similarly here (Diftara is more important than paper. People do not store it for a tax receipt, only for a Get, which is a bigger Shi'ur!)

Question (Ri): We should not have brought Abaye's teaching here! (Maharam - even without it, we can ask that the Shi'urim are different. Meginei Shlomo answers that the Shi'ur that Abaye taught was known to be bigger than a Kami'a.)

Explanation: Gevil is full hide, just the hairs were removed.

Support: In Bava Basra (3a), it says that Gevil is rocks that were not smoothed. This shows that something not prepared is called Gevil.

Explanation (cont.): When they divide [the hide] into two [layers], the part on the side of the hair is called Klaf, and the part on the side of the flesh is called Duchsustus.

Explanation (R. Tam): In Yevani (Greek), meat is called Sustus. "Duch" is a place, e.g. Duch Plan (Mekom Ploni). They call it Duchsustus, i.e. the place of the meat;

Our parchments have the law of Klaf, and we may write on them a Sefer Torah, Tefilin or Mezuzah, on the side of the meat;

Explanation #2: This is unlike the opinion that our parchments are Duchsustus, because the craftsmen who prepare them scrape off the top layer, and Duchsustus remains.

Rebuttal: If so, why may we write Tefilin on them? We conclude that Tefilin must be specifically on Klaf!

Opinion #1: Klaf and Duchsustus are not Afitz.

Question: If so, they would be Pasul for writing a Sefer Torah, Tefilin or Mezuzah, for we require a Sefer!

In Megilah (19b) we disqualify writing Megilas [Esther] on Diftara (a hide not Afitz) because [the Megilah] is called a Sefer. Below, it connotes that [Klaf and Duchsustus] are [for a Sefer Torah, Tefilin or Mezuzah]!

Question: Our parchments, which are not Afitz, why are they Kosher?

Answer (R. Tam): Our preparation is considered like Afitz.

Support #1: In Menachos (31b), it says that a tear [in the parchment] that goes through two [lines], it may be sewn. If it goes through three, it may not be sewn. Another Beraisa says that a tear through three lines may be sewn. If it goes through four, it may not be sewn. They do not argue. One is when it was Afitz, and the other is when it was not Afitz.

Inference: A Sefer Torah is Kosher even if it was not Afitz, i.e. when [the parchment] was prepared well, like ours.

Support #2: In Gitin (11a) regarding a [Persian] document, it says "we require something that cannot be forged!" (an erasure would be evident), and it answers that it was Afitz;

Inference: If it was not Afitz, it can be forged. We can testify that our [parchments] cannot be forged. This shows that [our parchments] are considered like Afitz.

Implied question: The Gemara could have asked a contradiction between the Reisha and Seifa of the Beraisa itself, and it connotes that it sought to challenge our Mishnah!

Answer (Ri): We find like this in Bava Metzi'a (37a) regarding "we ask a contradiction in Gezel... (A Mishnah in Yevamos says that if one does not know from whom he stole, and all of them claim from him, he leaves the theft in front of them, and goes away.) This is R. Tarfon's opinion";

[The Gemara continues] what is the source that our Tana is R. Tarfon? [A Tosefta] taught about that [Mishnah that R. Tarfon admits that if he told two 'I stole from one of you, but I don't know from which'; that he pays both]. It could have asked a contradiction between those two (the Mishnah in Yevamos, and the Tosefta that was taught about it), and [instead] it challenges the Mishnah in Bava Metzi'a.

Suggestion: We ask that since it mentions Klaf, this implies that Duchsustus does not (have this Shi'ur).

Rejection: If so, above that it answered 'what does "Mezuzah" mean? It is a Mezuzah (parchment) in Tefilin', we could still ask from our Mishnah, which teaches Klaf, and it implies that Duchsustus does not (have this Shi'ur), and the Beraisa gave the same Shi'ur (enough to write a Mezuzah) for Duchsustus like for Klaf!

Explanation: Rather, here it relies on the Beraisa above. (We needed to resolve that the Shi'ur for Duchsustus is to write a Mezuzah, and the Shi'ur for Klaf is to write Parshas Shma.)

Question: Why doesn't [the Gemara] say that both of them refer to Tefilin? Klaf is in the place of the hair, and Duchsustus is in the place of the skin!

Answer: It prefers to uphold the first answer, which said that it refers to Mezuzah. Indeed, it could have said that both of them refer to Tefilin.

Question: If Rav holds like R. Achai, he should say also that Klaf is like Duchsustus!

Answer: Rav explains that R. Achai's teaching [that if one deviated in either, it is Kosher] applies only to Tefilin.

Implied question: Why does it say "Kasvah" (he wrote it) teach in the feminine? (Tefilin is masculine!)

Answer: It refers to Mezuzah (a parchment) in Tefilin.

Question: A Mishnah in Megilah (8b) says that the only way that Seforim differ from Tefilin and Mezuzos is that Seforim are written in every language, and Tefilin and Mezuzos are written only in Ashuris;

Why doesn't it teach also that Tefilin and Mezuzos are written only on Gevil?

Answer (Ri): It did not teach this because they are not Pasul on Gevil for the same reason. Rather, this (Tefilin) requires Klaf, and this (Mezuzah) requires Duchsustus;

However, this that they require Ashuris is for the same reason. We expound there "v'Hayu" - they will be in their status (like in the Sefer Torah).

Answer #2: Also, even they (Tefilin and Mezuzah) are not the same. This (Tefilin) is written on Klaf, and this (Mezuzah) is on Duchsustus.

Question: It could have taught that Seforim are written on paper that was not erased. Specifically on erased paper a Sefer Torah is Pasul in Maseches Seforim (1:6);

However, Tefilin are written only on hide, like is proven below (108a)!

Strengthening of question: The Yerushalmi in Megilah (1:9, which says that Seforim may be written [one Parshah] on two hides (parchments), but Tefilin and Mezuzos may not. Even though it discusses on what they are written, it does not teach the Heter for paper that was not erased. We cannot say that the Tana omitted cases, for he said "the only differences between..."! Tosfos in Menachos disqualifies Seforim on any paper. Maseches Seforim disqualifies a Sefer on "paper"; the text should not say "erased" - Chasam Sofer.)

Question: Paper that was not erased should be Pasul for a Sefer Torah, like we disqualify Megilas Sotah (the scroll on which a Kohen writes the curses), because it says "Sefer"!

Answer: It was taught that paper is Pasul for Megilas Sotah, i.e. erased paper, even though it did not specify, like we find here regarding a Sefer Torah, that it taught Stam paper, and it refers to erased paper, like we say in Maseches Sofrim.

Implied question: Parshas v'Hayah Im Shamo'a is far from Parshas Shma! (How could we use them for a Mezuzah? There are other Parshiyos in between!)

Answer: [The Gemara says that if it were permitted to descend in Kedushah,] we could make [a Mezuzah from a Torah parchment], i.e. if Shma were written at the end of an Amud (column), one could write after (under) it Parshas v'Hayah Im Shamo'a in the margin, or if Parshas v'Hayah Im Shamo'a were written at the top of an Amud, one could write above it Parshas Shema.

Explanation (Ri): Rav's teaching was taught Stam in the Beis Midrash, that Klaf and Duchsustus are the same, and [the Gemara] initially thought that it was said regarding Tefilin. This Havah Amina could not be sustained, until [the Gemara] concludes now that it was said regarding Mezuzah;

The Beraisa above "if he changed regarding this or this, it is Pasul", both of these refer to Tefilin. The Sugya in Menachos (31b) is like the conclusion of our Sugya. (Maharsha - we could have explained that both refer to Mezuzah, when he wrote on the wrong side of Klaf or Duchsustus. Tosfos prefers to say that Menachos 31b is like our Sugya concludes. Our Sugya concludes like this in order to explain that one way is totally Pasul, i.e. Tefilin on either side of Duchsustus, similar to the answer above, that a Mezuzah on either side of Klaf is Pasul.)