Gemara

66b (R. Yirmeyah bar Aba) Question: If a man asked two to write and give a Get to his wife, and they asked a scribe to write it, and they signed it, what is the law?

Answer (Shmuel): If she remarried relying on this Get, she must leave her new husband. This law requires investigation.

Even though Shmuel said that the Halachah follows R. Yosi, that Mili cannot be transferred to another Shali'ach, Shmuel was unsure if the husband meant that they must sign it, or that they must write the Get itself.

Question: Shmuel holds that if 'write' means to sign, they can ask another to write the Get. Shmuel said that the Halachah follows R. Yosi, that Mili cannot be transferred to another Shali'ach!

Answer: If 'write' means to sign, it is as if he told them to appoint a scribe to write it. R. Yosi agrees that Omer Imru (telling someone to appoint a Shali'ach) works.'

87b (Mishnah): A Get in Kesav Yad Sofer (handwriting of a scribe) and signed by one witness is valid;

88a (R. Yirmeyah): The text of the Mishnah says 'Chasam Yad (signed by the) Sofer and one (other) witness is valid,'

(Rav Chisda): The Mishnah is like R. Yosi, who says that Mili cannot be transferred to another Shali'ach.

67b Question: If R. Yosi agrees that Omer Imru works, disaster may result! If one told two people to ask a scribe to write a Get, and to ask two others should sign it, they might ask the scribe to be a witness and sign, lest he be shamed (that he was not asked to sign). The husband did not authorize this (the Get is Pasul)!

Answer: L'Chatchilah, one may not ask two people to ask a scribe and witnesses to write and sign the Get, therefore we are not concerned for the above case.

Some permit this l'Chatchilah. They must say that R. Yosi holds that Mili cannot be transferred even regarding Omer Imru. Shmuel disagrees about Omer Imru.

86a: A Get with a date and one witness is Pasul. If she remarried based on it, the children are Kosher.

(Rav and R. Yochanan): This refers to a Get in the husband's handwriting.

Had a scribe written it, the children would be Mamzerim.

(Shmuel): The Mishnah discusses even when a scribe wrote it;

(Mishnah): A Get in Kesav Yad Soferf (the scribe's handwriting) v'Ed (and one witness signed) is a valid Get.

88a: R. Avahu was about to validate a Kesuvah based on witnesses who recognized Kesav Yad Sofer and the signature of one of the witnesses.

R. Yirmeyah: The text of the Mishnah is Chasam Sofer. (Kesav Sofer and one witness do not suffice.)

Rishonim

Rif and Rosh (49a and 9:9): The text of the Mishnah says Chasam Yad Sofer v'Ed. R. Avahu was about to validate a Kesuvah through Kesav Yad Sofer v'Ed. R. Yirmeyah told him that the text of the Mishnah is Chasam Sofer.

Ran (33a DH v'Afilu): Even though Shmuel holds that Omer Imru works, the Rif relies on the Sugya on 66b, which says that the text of the Mishnah is Chasam Sofer, which implies that Omer Imru does not work. BaHaG and R. Chananel agree. Sefer ha'Terumos rejects this proof. The Sugya did not rule like R. Yosi. Rav Ashi merely established the Mishnah like him. Even Shmuel agrees! No Amora explicitly argues with Shmuel. However, Tana'im argue about Omer Imru in a Mishnah (66b), and a later Mishnah (88a) is Stam (like R. Yosi), so we follow the Stam Mishnah.

Rebuttal (Gra EH 120:14): Amora'im may rule against a Stam Mishnah (even if it follows an argument. Perhaps we follow Shmuel!)

Rambam (Hilchos Gerushin 9:27): If one told 10 people to write, sign and give a Get, one writes, two sign and one gives. Even if the one who wrote the Get was one of the two witnesses and gave it, it is Kosher.

Question (Ran, ibid.): The Rambam (2:6) is unsure whether or not the Halachah follows Shmuel. If so, why is he Machshir Chasam Sofer and one witness?! Perhaps it is because the Gemara said that it is Kosher, but one may not do so (lest disaster result). In particular, we do not allow Omer Imru due to Safek, so there is no concern. I am not satisfied. Perhaps some are sure that Omer Imru works, and disaster will result! Rather, we should be stringent about both laws due to Safek. The Ri and Ramban say so.

Answer (Kesef Mishneh): Since there is an argument about this in the Gemara, we are not concerned lest one be sure that it works. It seems that the Rambam does not permit the scribe to be one of the witnesses l'Chatchilah, but if he signed, one may give the Get.

Mishneh l'Melech: Also ha'Rachash (3) says that the Rambam never allows the scribe to be one of the witnesses l'Chatchilah. This is wrong. Here, because he told 10, he prefers that each part of the Shelichus be done by different people. This is why the Rambam added 'and he gave the Get'! Normally, the scribe may be one of the witnesses l'Chatchilah. In Halachah 2:6 (and 9:31), the Rambam says that if one told two to write and sign (and give) a Get, they do so themselves, i.e. l'Chatchilah.

Tosfos (88a DH Omar): We do not learn from R. Yirmeyah that Chasam Yad Sofer v'Ed is Kosher, for all the Amora'im (66b) who allow Omer Imru must disqualify it.

Rosh (9:6, citing the Ri): Even though the Halachah follows Rav against Shmuel in Isurim, since all the Amora'im (66b) who allow Omer Imru must disqualify Chasam Yad Sofer v'Ed, due to concern for disaster, like Shmuel, we follow them. R. Chananel says that we follow Rav Ashi (71b), who disqualifies Omer Imru. This is no proof! Rav Ashi merely established the Mishnah like R. Yosi! Perhaps R. Chananel meant that we are stringent to disqualify Omer Imru, but he also disqualifies Chasam Yad Sofer v'Ed.

Poskim

Shulchan Aruch (130:18): One should be careful that the scribe not sign to be a witness, for some disqualify.

Beis Yosef (DH v'Chosav ha'Rosh): Sefer ha'Terumos, the Ran, the Ramban, Semag, Semak and the Rashba are stringent like the Ri.

Beis Yosef (DH veha'Mordechai...): The Mordechai says that perhaps the Rif and R. Chananel, who disqualify Omer Imru, also disqualify Kesav Yad Sofer v'Ed. This is difficult, for the Rif establishes our Mishnah to be Machshir, like R. Yirmeyah! Perhaps he means that the Rif is Machshir only b'Di'eved. We must explain the Rosh this way. Also the Rosh establishes our Mishnah to be Machshir, and he cited the Ri and did not argue, and in Teshuvos (45:8,28) he rules like the Ri. The Mordechai says that the Ri relied on R. Chananel to be Machshir a child from such a Get. He was unsure what the Ri would say before she remarried, or after Nisu'in without children. The Rivash (206) says that it is like all Pasul Gitin. She may not remarry; if she did, she need not leave.