Shamai's error is based on the Mishnah in Nedarim concerning the episode that took place in Beis Choron - where the son of a man whose father was Mudar Hana'ah from his property, was about to get married. Having arranged the Se'udah in his own Chatzer ...

... he donated them to his friend, to enable his father to participate.

The friend promptly declared the gift Hekdesh.

When the donor complained that that was not what he gave it to him for, he replied that - it was clear that he only gave him the gift so that he and his father could sinfully make amends at his expense (since was the Shali'ach).

The Chachamim declared that - 'If a Matanah is not valid to the extent that the recipient has the right to declare it Hekdesh, then it is not a Matanah'.

Consequently, had his father participated in the Se'udah under those circumstances - the son would have transgressed the La'av of "Lo Yachel Devaro".

Shamai based his complaint - on the principle that we just discussed. He understood that in the case of Yonasan ben Uziel too, since the owner did not wish his children to receive his estate, this would preclude Yonasan ben Uziel from giving it to them, in which case, the gift should be null and void.

His mistake lay in the fact that - as opposed to the current episode of Beis Choron, the donor did not stipulate with Yonasan ben Uziel that he was to refrain from giving the property to his sons, in which case, there was nothing to prevent him from doing so.

Hillel ha'Zakein had - eighty Talmidim.

The first thirty were worthy for the Shechinah to rest on them like Moshe, but it didn't - because their generation was not worthy.

There were twenty in the middle. The other thirty were on the level - of stopping the sun in the sky like Yehoshua (and Moshe) did.

The ...

... greatest of them all was - Yonasan ben Uziel (see Rabbeinu Gershom).

... smallest of them all was - Rebbi Yochanan ben Zakai.

There doesn't seem to be much that Rebbi Yochanan ben Zakai did not know: He knew T'nach, Mishnah and Agados (Medrashim, such as Tanchuma and Medrash Rabah). When the Tana says ...

... 'Gemara', he means - the understanding of the sayings of the earlier Tana'im by the later ones (even though the era of the Gemara per se had not yet even begun).

... 'Halachos', he means - Halachos le'Moshe mi'Sinai.

... 'Dikdukei Torah', he means - extra letters, which come sometimes to include and sometimes to exclude, depending on the context.

... 'Dikdukei Sofrim', he means - the Rabbinical decrees that Chazal issued (to prevent the transgressing of Torah laws).

He knew all the Kal va'Chomers, the Gezeiros Shavos and Gematriyos (incorporating the acronyms). 'Tekufos' refers to - the reckoning of the movement of the sun and the moon (for the purpose of working out Rosh Chodesh and the formation of leap years).

He was also conversant with the speech of the angels and of the demons (to make them swear to him and do his bidding). And he could tell the future from the movement of the branches and the leaves of a palm tree (on days when the wind was not blowing). 'Mishlos Kovsin' and 'Mishlos Shu'alim' are - words of reprimand couched in parables of laundry-men and foxes (respectively).

Finally, 'Davar ...

... Gadol' means - 'Ma'aseh Merkavah' (which Yechezkel saw, and which serves as the basis of Kabalah) and Davar ...

... Katan' - the 'Havayos de'Abaye ve'Rava' (all the She'eilos asked by the Amora'im, which had already been asked by the Tana'im, but had subsequently been forgotten).

The above describes the greatness of Rebbi Yochanan ben Zakai. Yonasan ben Uziel was even greater, inasmuch as - in addition to all the above, when he studied Torah, the angels would come to listen, and any bird that flew past would get burned from their fire.

Our Mishnah rules that if Reuven says about Shimon ...

... 'Zeh B'ni' - he is believed.

... 'Zeh Achi' - he is not believed.

This does not mean that (in the latter case) Shimon receives nothing. In fact, he receives the portion that Reuven admits is his (for example, if there is a third brother who queries Shimon's (unproven) relationship, and there are three fields, then the third brother takes one and a half fields (as if there were only two brothers), Reuven takes one, and Shimon, the remaining half).

The Tana then states that if Shimon dies, the property then reverts to where it came from (to Reuven). When he talks about property that 'fell to him from somewhere else', he means - property that he either purchased or inherited.

The third brother gets to share that property with him when Shimon dies - on the basis of Reuven's admission that he was a brother.

We refute Rav Yehudah Amar Shmuel, who explains 'Zeh B'ni, Ne'eman' to mean that he is an heir and will inherit part of the Yerushah - because it is obvious, seeing as he is able to give it to him as a Matanah (as we have already learned).

We cannot answer that we need the Tana to teach us that he is believed even regarding property that he has not yet acquired (Ra'uy) - because then he is in fact not believed.

We did indeed learn earlier that (based on the Pasuk "Yakir") a father is believed even as regards property that he acquired afterwards or on his death-bed - but that D'rashah is confined to the Cheilek Bechorah (where we know that basicaly he is a son).

Rav Yehudah Amar Shmuel also explains that 'Zeh B'ni' is believed 'li'Fetor es Imo mi'Yibum'. In spite of the Mishnah in Kidushin 'Mi she'Amar be'Sha'as Miysaso' Yesh li Banim, Ne'eman' this is not obvious - because that Mishnah is speaking about a case where we do not know that he has a brother, whereas our Mishnah speaks even when we know that he has.

The S'vara to differentiate between a case where we know that he has a brother and one where we don't is that - in the latter case there is a 'S'fek S'feika' (maybe he has no brothers, and even if he does, maybe he has a son, in which case, when the father says 'Zeh B'ni' he is merely substantiating the Chazakah); consequently, his wife will be permitted to marry anyway.

Even if a man subsequently claims to be a brother of the deceased - he will not be believed, and the widow will not even require Chalitzah.

In the case in our Mishnah - the father will only be believed to say 'Zeh B'ni' against a Chazakah that he has a brother but not if there are witnesses who testify to that effect.

Even though someone who declares 'Yesh li Banim' is also believed, our Mishnah presents the case of 'Zeh B'ni' is - to balance the Seifa 'Zeh Achi, Eino Ne'eman', where he wants to add 've'Yitol Imo be'Chelko' (which only makes sense if he actually identifies him).

Rav Yosef quoting Rav Yehudah Amar Shmuel explains that a man is believed to say 'Zeh B'ni' because he is believed to say 'Gerashti es Ishti'. Rav Yosef himself queries this however on the grounds that - the latter is a Mishnah, whereas the former is no more than a statement of Amora'im, and Shmuel would not have given a reason for something that does not have a source based on something that does.

The significance of Rav Yosef querying his own quotations is that - he became ill and forgot many things that he learned from Rav Yehudah his Rebbe. That is why he often queries some of his own statements, and has to amend them so that they make sense.

What Rav Yehudah Amar Shmuel really said was that - 'Zeh B'ni' is believed (to exempt his wife from Yibum), because of 'Ho'il' (the 'Migu' that he could have given her a Get [as we explained earlier]) ...

... on which Rav Yosef commented - now that we say 'Ho'il', we believe a husband who claims that he divorced his wife with a 'Migu' too (because he could have given her a Get had he wanted).

When Rav Yitzchak bar Yosef Amar Rebbi Yochanan said 'Ba'al she'Amar Gerashti Eino Ne'eman', Rav Sheshes reacted - by blowing in his hand and commenting that 'Rav Yosef's 'Ho'il has gone' just like that ...

... despite the 'Migu' - because had his claim had any validity, there should have been a 'Kol' (rumor) to that effect.

We reconcile this ruing with Rebbi Chiya bar Avin, who quoted Rebbi Yochanan as saying 'Ne'eman' (like Rav Yehudah Amar Shmuel) - by establishing the latter ruling from now on (but not retroactively).

By 'mi'Ka'an u'le'Haba' we mean that - he either claimed to have divorced his wife 'S'tam', or that he specifically said 'from today' (but not when he gives an earlier date).

The ramifications of the She'eilah whether he is believed retroactively or not will be - in a case where he claimed that he divorced his wife two week's earlier and in the interim she committed adultery. If he would have been believed retroactively, then she would be Patur from Misah, whereas now that he is not, she is Chayav.

We ask what the Din will be in a case where the husband claims that he divorced his wife previously - whether we accept the principle 'Palginan Dibureih' (to believe him from now on even though we do not believe him retroactively, because, when all's said and done, he could give her a Get now), or whether we do not.

And we cite Rav Mari and Rav Z'vid - who argue over this very point.

We query one of the opinions from a statement of Rava, who ruled that in a case where a man testifies that P'loni committed adultery with his wife - we accept his testimony vis-a-vis 'P'loni', who will be sentenced to death, provided there is an additional witness (in spite of the fact that he is not believed vis-a-vis his wife).

The basis of Rava's ruling is - the principle 'Palginan Dibureih'.

We reconcile Rava with the opinion that does not accept 'Palginan Dibureih' in our case - by confining his ruling with regard to dividing a testimony that concerns two people, but not to divide a statement pertaining to one person into two time-periods.