Answer #1 (Rav Sheshes): This shows that contradiction is the beginning of Hazamah (disqualifying witnesses through testimony of other witnesses that at the time the first witnesses say that they saw the testimony, they were elsewhere).

Just like Hazamah is only in front of the witnesses, also contradiction must be in front of them.

Objection (Rav Nachman): If David and Levi were here and contradicted these latter witnesses, we would have contradictory testimony, and one could not collect with this document.

In our case David and Levi are not here, and if they would be here, perhaps they would admit. Do we rely on David and Levi (and allow one to use the document)?!

Answer #2 (Rav Nachman): The latter two witnesses counter the former two, and we leave the money (or property) in its Chazakah with its current owner (the alleged borrower or seller).

This is like the property of Bar Shatya (a man who alternated between sanity and insanity).

Bar Shatya sold property. Two witnesses said that he was insane at the time (so the sale is invalid). Two others said that he was sane at the time.

(Rav Ashi): Two witnesses counter the other two, and the property stays in the possession of Bar Shatya.

This applies only to property he inherited, but not if he himself bought property and now sold it. (There is no Chazakah that it is his.) Perhaps he was insane when he bought it!

(R. Avahu): Hazamah of witnesses can only be in their presence. They can be contradicted in their absence.

If Hazamah is done in their absence, it is not considered Hazamah, but it is contradiction.

(Beraisa (19b)): If (other) witnesses know that these are their signatures, or if there is another document which they signed which was contested and validated by Beis Din, they are not believed (to say that the witnesses on a document were invalid).

Inference: Another document may be used to validate only if it was disputed. This supports R. Asi.

(R. Asi): We validate a document only from a document that was disputed and validated by Beis Din.

(Chachamim of Neharda'a): We validate a document only from two Kesuvos or from two documents of sale of fields that the buyers used for three years without protest.

(R. Simi bar Asi): This applies only if the documents are held by others, and not by the bearer of the document we wish to validate;

The bearer may not validate it from documents he holds, lest he copied the signatures.

Question: The same concern applies to documents held by others. Perhaps he saw them and imitated the signatures!

Answer: We are concerned that he could imitate them so well only if he has the documents.

(Beraisa): A person may write in a document testimony that he saw, and (orally) testify based on it many years later.

Opinion #1 (Rav Huna): He can testify only if he remembers (some of) the testimony by himself.

Opinion #2 (R. Yochanan): He can testify even if he does not remember it by himself.

(Rabah): We learn from R. Yochanan that if two witnesses saw testimony and one forgot it, the other may remind him.

Question: May a party in the case remind a witness of the testimony?

Answer #1 (R. Chaviva): Yes.

Answer #2 (Mar bar Rav Ashi): No.

The Halachah is, he may not;

If the witness is a Chacham, he may testify even if the claimant reminded him.

Rav Ashi knew testimony for Rav Kahana, but forgot it, even after Rav Kahana tried reminding him of it. Later, he remembered and testified for him.

Rav Kahana was taken aback that Rav Ashi was testifying for him.

Rav Ashi: Don't worry, I'm not relying on what you said. I put my mind to it and remembered.

(Mishnah): Mounds that are close to the city or the road are Tamei, whether they are old or new;

Old far mounds are Tamei, and new ones are Tahor;

(R. Meir): Within 50 Amos is considered close. Sixty years old is considered old;

(R. Yehudah): If there is no closer one, it is called close. If no one remembers before it was built, it is old.

Question: What do 'city' and 'road' refer to?

It cannot refer to the simple meaning, for mi'Safek (without a source) we do not presume that there is Tum'ah!

(Reish Lakish): An excuse was found to be Metaher Eretz Yisrael.

Answer (R. Zeira): Rather, 'city' is a city near a cemetery, and 'road' is a road to a cemetery.

Question: We understand why the mound on the road is Tamei. Sometimes there is not enough time before Shabbos to get to the cemetery, and the body is buried in the mound;

But if a city is near a cemetery, why is a nearby mound Tamei? Everyone would go to the cemetery!

Answer (R. Chanina): Women bury miscarriages in mounds, and lepers bury limbs that fell off;

Up to 50 Amos, a woman would go alone (and the Tum'ah would be unknown). More than 50 Amos, she would get an escort, and go to the cemetery. Therefore, in Eretz Yisrael we do not assume that they are Tamei.

(Rav Chisda): We learn from R. Meir that a person remembers testimony for 60 years, but no longer.

Rejection: This is not so. It is not incumbent on a person to remember Tum'ah in a mound. He has a responsibility to remember testimony, so he (puts it to heart and) remembers it longer.

(Mishnah): If both witnesses on a document say that they recognize both signatures, they are believed;

Rebbi says, if each recognizes only his own signature, we need another witness who recognizes both signatures;

Chachamim say, this is not needed. A person is believed to verify his signature.