In a case where Reuven and Shimon both claim that a certain field belonged to their respective fathers and where Reuven brings witnesses to that effect, whereas Shimon brings witnesses that he worked in the field for three years, Rabah believes the latter - because he has a 'Migu', since he could have claimed that he bought the field from Reuven and has now made a Chazakah on it.

Abaye disagrees with him on the grounds that - it is a 'Migu be'Makom Eidim', since there are witnesses who refute his claim, who testify that the field belonged to Reuven's father. Consequently, it is a 'Chazakah she'Ein imah Ta'anah'.

Shimon subsequently conceded - that the field had indeed belonged to Reuven's father and that he purchased it from him. And when he initially claimed that it belonged to his own father, he meant - that it was established by him as if he had inherited it from him.

Ula accepted his second argument. The Neherda'i ruled -'Ein To'en ve'Chozer ve'To'en' (a litigant does not have the right to amend his initial statement).

Had Shimon originally added that the field originally belonged to his father and not to Reuven's, Ula would not have accepted his second claim - because it is only in the previous case, where Shimon's second claim clashed slightly with his first, that Ula holds 'Chozer ve'To'en', but not where it contradicts it completely.

In the earlier case, Ula did not require Shimon to bring a proof that his father owned the field at least for one day, like a Yoresh who proved that he had worked in the field that he (claimed to have) inherited from his father for three years - because unlike the latter case (where the Yoresh did not make any other claim to substantiate his Chazakah), Shimon did (when he claimed to have purchased the field from Reuven's father).

Ula would have also conceded that Shimon is not believed, had he left the courtroom before returning and amending his original statement - because then we would suspect that friends or relatives prompted him to amend his original statement.

For the Neherda'i to have accepted Shimon's second statement, he would have had to claim - that his father purchased the field from Reuven's father (because that would hardly clash at all with his initial statement).

And they would have also accepted Shimon's second statement if his first statement had been made outside Beis-Din (even if his second claim completely contradicted the first one) - because a person is justified in declining to reveal all his arguments outside Beis-Din (so as not to assist his disputant in presenting his case).

This would not be the case however - if Shimon were to actually admit liability in front of two witnesses, in which case Beis-Din would obligate him to pay.

The Halachah is like Ula in the latter's Machlokes with the Neherda'i, because Ameimar supports him - despite the fact that he (Ameimar) himself was from Neherda'a.

In a case where Reuven and Shimon both claim that the field belonged to their respective fathers, Reuven brings witnesses that he worked in the field for three years, and so does Shimon, only Shimon's witnesses also bear out his original claim - Rav Nachman rules like Shimon - because, although the two testimonies as to who made the Chazakah cancel each other out, the testimony that the field originally belonged to Shimon's father remains intact.

Rava objected to Rav Nachman's ruling - in that, seeing as one of the pairs of witnesses has been proven false, Beis-Din can no longer accept any aspect of their testimony.

Rav Nachman however insists - that since Shimon's witnesses presented two separate pieces of testimony, the one that has not been contradicted remains intact.

In a case where two pairs of witnesses contradict each other, Rav Huna authorizes each pair to testify in other lawsuits. The case is - where the first pair testify that Reuven lent Shimon a Manah on a specific date, whilst the second pair testify that no such loan took place, since Reuven was with them that entire day.

The Torah only believes the latter pair of witnesses and declares the former pair 'Eidim Zom'min' - there where the second pair refute the testimony of the first pair on the grounds that they were with them on that day (but not when they claim that it was the debtor or the creditor).

Rav Huna does not however, permit one witness from each pair to testify as one pair in other lawsuits - because one of the witnesses is definitely a swindler, unlike the current case, where one of the pairs is honest, so as long as they do not testify together, we place them on a Chezkas Kashrus.]

Rav Chisda says - that once a pair of witnesses has been contradicted, they can no longer be accepted under any circumstances.

We reconcile Rava (who, in the previous case, discounts the testimony of witnesses who have been contradicted completely) with Rav Huna - by drawing a distinction between accepting part of the same testimony on which they were contradicted (Rava) and their acceptance in other lawsuits (Rav Huna).

We cannot, however, reconcile Rav Nachman (who validates that part of the witnesses' testimony that was not contradicted) - with Rav Chisda.

When Reuven (whose witnesses only testified on his Chazakah) subsequently bring witnesses that the field previously belonged to his father - Rav Nachman retracted from his previous ruling (from placing ruling in Shimon's favor, to a Safek (see Tosfos DH 'Anan Achsinan').

Rava (or Rebbi Zeira) queries him from a Beraisa. In a case where two witnesses testify that Reuven died and two other witnesses testify that he is still alive, or the same two pairs of witnesses argue over whether his wife is divorced or not - the Tana Kama forbids his wife to remarry Lechatchilah, but permits them to remain together if they are already married.

The two ramifications of the latter case are - a. to exempt her from Yibum, in the event of Reuven's death, and b. to permit her to remarry immediately, even in Reuven's lifetime.

In the former case, despite the fact that their marriage involves a Safek Kareis, which carries with it a Chiyuv Asham Taluy, we permit ...

... the man to stay married to a Safek Eishes Ish - only if he is one of the witnesses who testified that her husband died.

... the woman to remain married - because she claims to be sure that her husband is dead.

Rebbi Menachem b'Rebbi Yossi rules that even if they are already married, she must leave her husband - which he then qualifies by restricting it to where the second pair of witnesses testified before they got married, but if they testified only afterwards, they may remain married ...

... to avoid making a mockery of Beis-Din (who one minute permit her to marry, and then rescind their permission).

This Kashya initially affected Rav Nachman's imminent ruling in the previous case - causing him to reconsider his second ruling (retracting from the initial one).

He then acted strangely - by leaving Beis-Din and going ahead with his original intention of placing the property before both Reuven and Shimon (as Tosfos explained there).

The Chachamim thought that he must have made a mistake and forgotten the Beraisa.

Rav Nachman did not make a mistake however. He went ahead with his original plan - because he found other Tana'im who argued with Rebbi Menachem b'Rebbi Yossi and who were not concerned about 'Zilusa de'bei Dina' (as we shall now see).

Rebbi Yehudah rules 'Ein Ma'alin li'Kehunah al-Pi Eid Echad'. This statement incorporates not eating Terumah, not serving in the Beis-Hamikdash - and not Duchening (Birchas Kohanim).

Rebbi Elazar confines Rebbi Yehudah's ruling to where there are Or'rin - protestors, witnesses who claim that he is not a Kohen. Otherwise, he holds 'Ma'alin li'Kehunah ... '.

Raban Shimon ben Gamliel quoting Rebbi Shimon ben ha'Segan states - 'Ma'alin li'Kehunah al'Pi Eid Echad' (which obviously speaks where there are no Or'rin), seemingly duplicating Rebbi Elazar's ruling.

We cannot establish the Machlokes (between Raban Shimon ben Gamliel quoting Rebbi Shimon ben ha'Segan and Rebbi Elazar) in a case where the 'Or'rin' of Rebbi Elazar consists of only one witness, which Rebbi Elazar accepts, but Raban Shimon be Gamliel rejects - because, as Rebbi Yochanan has taught, it is unanimously agreed upon that Ir'ur must consist of at least two witnesses in order to be effective.