Our Mishnah discusses a case where the house fell on a man and his wife, and we do not know for sure who died first. The triple bone of contention between the man's heirs and his wife's is who inherits a. the wife's Kesubah, b. her Nichsei Milug and c. her Nichsei Tzon Barzel.

Nichsei Milug and Nichsei Tzon Barzel are both what the wife brings into the marriage, only whereas the former is not inserted in the Kesubah, and the husband does not accept responsibility for it, the latter is inserted in the Kesubah and the husband takes responsibility for it.

The Tana must be speaking where they are no common children - because if there are, then it is they who wil inherit their mother's property, and not her father's heirs

When Beis Shamai say 'Yachloku', they are referring to all of the above (though some say in Yevamos that even according to Beis Shamai, the Kesubah remains in the Chazakah of the Yorshei ha'Ba'al).

It is the ...

... husband's heirs who inherit the woman's Kesubah.

... the father's heirs who inherit the Nichsei Milug.

And when Beis Hillel say 'Nechasim be'Chezkasan', they are referring to - the Nichsei Tzon Barzel.

Rebbi Elazar explains 'be'Chezkasan' of Beis Hillel to mean in the Chazakah of the woman's heirs. According to Rebbi Yochanan, he means - in the Chazakah of the father's heirs.

The basis of their Machlokes is that - on the one hand, the property belongs to the wife, since she brought it with her from her father's house, whilst on the other, it belongs to her husband, inasmuch as he took responsibility for it.

Resh Lakish in the name of bar Kapara rules that - Nichsei Tzon Barzel 'Yachloku'.

The Beraisa cited by bar Kapara says that - 'since each one comes to inherit (with a valid argument), Yachloku'.

Our Mishnah now discusses a case where the house fell on Yosef and his mother Rachel, and again, it is not clear who died first. Those who are now arguing over who died first are - Rachel's heirs (her paternal brothers) and her husband's heirs (his son [Reuven]).

According to the Tana Kama, even Beis Hillel concede here that 'Yachloku' - since, due to the fact that Ya'akov, Rachel's husband died before her, both sets of heirs come with an equal claim (not like in the previous case, where one comes as an owner, and the other, with a Sh'tar, claiming that the property is Meshubad to him).

If Rachel had another son [Binyamin] from another man, who was now arguing with Reuven over who died first - Binyamin would inherit the disputed property and not Reuven, because he is a Vadai Yoresh (all the property, if Ya'akov died first, and half the property, if Rachel died first), whereas Reuven is only a Safek (Yosef's portion, in the event that Rachel died first) and we have a principle 'Ein Safek Motzi m'Yedei Vadai'.

Rebbi Akiva disagrees with the Tana Kama. He holds that here too, Nechasim be'Chezkasan'. Despite the fact that he has not spoken earlier in this Sugya, he says 'Modeh Ani' - because the Tana Kama used the same expression.

Following Rebbi Akiva's statement, ben Azai commented that - he was already upset that Beis Shamai and Beis Hillel in the previous Mishnah, disagreed. And now, when Rebbi Akiva's colleagues at last found a case where they agreed, he had to come along and convert even that into a Machlokes!

Rebbi Ila interprets 'be'Chezkasan' of the Tana Kama to mean 'be'Chezkas Yorshei ha'Eim'. Rebbi Zeira holds - 'be'Chezkas Yorshei ha'Ben'.

The reasoning of ...

... Rebbi Ila is the fact that - once the husband dies, the property enters the Chazakah of the tribe of his wife's father, and that is where it ought to remain.

... Rebbi Zeira because - once the husband dies, his son automatically stands to inherit his father's property, before his wife's family, and so, it is his Yorshim who ought to inherit it.

Rebbi Zeira changed his mind, to hold like Rebbi Ila - after he arrived in Eretz Yisrael, which prompted him to declare that the very air of Eretz Yisrael makes a person wise.

Rebbi Simlai extrapolated from the fact that ben Azai said to Rebbi Akiva 'she'Basa ... ' that - he had advanced from being a Talmid of Rebbi Akiva to becoming a Talmid-Chaver.

Otherwise, he should have said 'she'Ba Rabeinu'.

They sent from Eretz Yisrael 'Ben she'Lavah be'Nichsei Aviv be'Chayei Aviv, u'Meis, B'no Motzi mi'Yad ha'Lekuchos'. The problem with this statement is that - if a son borrowed from his father, why is he claiming anything, and besides, how does the purchaser come into the picture?

We therefore amend it - by changing 'Lavah' to 'Machar'.

This statement does not belong in this Sugya. It really belongs earlier after the Mishnah of 'Nafal ha'Bayis alav v'Al Aviv', which we will shortly cite in connection with it.

The basis of the ruling is - the fact that the son sold the field in his father's lifetime, when it was still Ra'uy, and just as one cannot be Meshabed something that is Ra'uy, so too, can one not sell it.