Gemara

165b (Mishnah): If a document '100 Zuz' above, and it says 200 below (in the recap of the document), or vice-versa, we follow what is below.

We write the top so that if a letter is erased from the bottom, we can learn from the top.

166b (Rav Papa): If above it says 'Sefel' and below it says 'Kefel', we follow the bottom.

Question (Rav Papa): If it says 'Kefel' above and 'Sefel' below, what is the law? (Do we follow the bottom, or) do we suspect that the 'Kuf' should be a 'Samech', and some of the ink was moved by a fly?

This question is not resolved.

105b (Rav): If one sold 'for Istira (96 Perutos), 100 Ma'os', the buyer owes 100 Ma'os. If he sold 'for 100 Ma'os, Istira', he owes Istira.

173a (Mishnah): If Levi found a note saying 'the document of Yosef ben Shimon was paid', he cannot collect a loan from either man of this name.

Inference: Had he not found this receipt, he could have collected.

Contradiction (Mishnah): No one can use a document to claim money from either Yosef ben Shimon.

Answer (R. Yirmeyah): The case is, the loan documents have the grandfather's name (proving to which one he lent).

(R. Hoshaya): The case is, the loan documents have the grandfather's name, but the receipt does not.

Bava Metzia 102a (Mishnah): If Reuven rented a house to Shimon for a year and it was made a leap year, Shimon need not pay extra for the extra month. If he rented it for 12 months, he must pay for the added month. A case occurred in which one rented for 12 Dinarim for the year, a Dinar per month. R. Shimon ben Gamliel and R. Yosi ruled that he pays half for the added month.

102b (Shmuel): This is when they come to Beis Din in the middle of the 13th month. If Reuven said at the beginning of the month 'you must pay extra for this month', Shimon must pay for the entire month. If Reuven made no claim until the end of the month, Shimon is exempt.

(Rav Nachman): The owner is Muchzak in his land. (Even if Levi claims at the end of the month, Yehudah must pay.)

He is unsure which phrase we follow. Even if the phrase favoring the renter was said last, the owner is Muchzak and the renter must pay.

Rishonim

Rif (50b and Bava Metzia 59b): The Halachah follows Rav Nachman. The same applies to '100 Ma'os, Istira.' We follow the lesser clause, for property is in the owner's Chazakah, and the other is ha'Motzi mi'Chavero Alav ha'Re'ayah. If he seized, he keeps it, for now the other is ha'Motzi mi'Chavero. This refers to Metaltelim. Land is in the owner's Chazakah.

Nimukei Yosef (76b DH v'Shover): The Ro'oh holds that regarding a receipt, we assume the higher amount and ha'Motzi mi'Chavero Alav ha'Re'ayah. His Talmid, the Ritva, disagreed.

Rif (Kesuvos 47a): If a document gives Ne'emanus to the borrower, i.e. he wrote 'if you will say that you paid this, you will be believed', the stipulation is valid. If the borrower died, his heirs are believed to say that their father paid, for he did not need to tear the loan document or get a receipt. He relied on the Ne'emanus. However, the borrower must swear. Since the lender did not write 'you ae believed even without an oath', we are concerned lest he believed him to nullify the document to make it a Milveh Al Peh. The bearer of the document has the lower hand. Rav Hai Gaon said so.

Rambam (Hilchos Malveh 27:15): If above it says 'Sefel', and below it says 'Kefel', we follow the bottom, for it is less. If it says 'Kefel' above and 'Sefel' below, we suspect that the 'Kuf' should be a 'Samech', and some of the ink was moved by a fly. He collects only the smaller measure of Kefel. The same applies to all similar cases. The bearer of the document has the lower hand.

Rosh (Teshuvah 76:2): If Reuven brought a loan document against Shimon dated 'Nisan 5', and Shimon has a receipt dated Nisan 5 saying that Reuven pardoned to him all debts until this date, Reuven collects. Since it says until this day, this day is not included. The way people speak, 'until' does not include the day itself. Had the receipt said 'until now', it would be a Safek whether he pardoned before or after the loan given that day. We do not make one pay due to Safek. We assume that the loan was first.

Poskim

Shulchan Aruch (CM 42:8): In all these cases that we say that the bearer has the lower hand, if he seized Metaltelim, we do not take them from him.

Beis Yosef (DH u'Mah she'Chosav v'Iy): The Rif says so (Bava Metzia 59b). The Ramban explains that this is when the borrower willingly gave the larger amount to the bearer. Hagahos Maimoniyos (Hilchos Malveh 27:300) explains that the bearer has the lower hand due to ha'Motzi mi'Chavero. Now that the bearer seized, the borrower is the Motzi. The Magid Mishneh (27:16) says that this is even if he seized in front of witnesses.

Rema: All the more so, regarding a receipt we say that the bearer has the upper hand, for he is Muchzak. This is unlike those who disagree and say that even regarding a receipt, he has the lower hand.

Beis Yosef (DH v'Dikdek, and Bedek ha'Bayis): Maharik says that even when the bearer is Muchzak, he has the lower hand. If he saw the Meforshim I cited above, I do not know how he argued with them.

Shach (18): There is no argument. Maharik discusses one who was obligated without a document to give to Tzedakah according to his wealth. He claims that he need pay for redeeming captives only like everyone else, for a document specified that all will pay equally. Maharik said that redeeming captives is not included in Tzedakah, therefore, the bearer has the lower hand, even though he is Muchzak. His Chazakah does not help, for he seeks to uproot Torah law through the document. His Safek (that redeeming captives is included in Tzedakah) does not uproot his Vadai obligation. Here, the lender says that even without the document, Vadai he owes me, therefore seizure helps even in front of witnesses. Likewise, one who holds a receipt says that he is exempt even without the receipt. Therefore, since he is Muchzak, he has the upper hand. The same applies to Teshuvas ha'Rosh. Shimon claims that Reuven explicitly pardoned also the document in question. The Ritva cited in the Nimukei Yosef agrees that the bearer of a receipt has the upper hand, since he is Muchzak. He argues only about a receipt that says only 'Dinarim', for this connotes only two. This is why the Nimukei Yosef cited the Ritva regarding the Sugya of a document that says Dinarim. Also, we could say that the Rosh and those who say that seizure helps discuss seizure before the Safek arose, or seizure with permission, and he need not have a Vadai claim.

SMA (23): Since seizure helps even without Reshus, all the more so a receipt helps, for he is Muchzak with Reshus. However, we hold that an unclear receipt does not help against a clear document with a lien against land. If not, the Rif and Tur contradict themselves! (Here they say that seizure helps. In Kesuvos and 71:34,) they say that if a lender gave Ne'emanus, the borrower must swear, for he was trusted only to nullify the document, but it is still a Milveh Al Peh. This is because the lender holds a clear document. This is difficult for the Beis Yosef, who says that regarding pardon, we do not attribute to flies, for ha'Motzi mi'Chavero Alav ha'Re'ayah.

Shach (17): The Beis Yosef is correct. We write a receipt to nullify a document, therefore, a receipt has the upper hand against a loan document. After the loan document is Batel, the bearer of the receipt has the lower hand regarding swearing (he must swear). This is not because the loan document is clear, for the receipt nullified it! Surely we tear the loan document once we hear that it was paid! The borrower must swear Heses, just like he must swear to counter a verbal claim. Likewise, one who seized must swear Heses.

Taz: There, the borrower is exempt only due to the lender's pardon. He cannot say 'you trusted me even without an oath.' One does not know what is in another's heart! Therefore, the lender is believed to say what he intended. A receipt breaks a document. It is like an erasure. If it is not known what was erased, this ruins the document. The following is difficult. The Shulchan Aruch (49:8) rules like the Ramah, that if there are two Yosef ben Shimon's in a city, and a loan document gives the grandfather's name to distinguish them, but the receipt does not, the one holding the receipt must pay. The Tur exempts. It seems that the Tur rules like the first opinion in the Rema here, and the Ramah holds like the latter opinion. The Rema (who favors the first opinion here) should have argued with the Shulchan Aruch there! I say that the Tur's opinion is primary, for ha'Motzi mi'Chavero Alav ha'Re'ayah.