Yevamot

And [in connection with this] Resh Lakish stated: No possession is ever acquired,  unless the testator had said, 'Let X and Y inherit this and that particular field which I have assigned to them as a gift, so that they may inherit them'.  And the third  is his ruling in connection with the following Mishnah:  If a man assigned all his estate, in writing, to his son  [to be his]  after his  death, the father may not sell it  because it is assigned to the son, and the son may not sell it because it is in the possession of the father. If the father sold the estate, the sale is valid until his death.  If the son sold it, the buyer has no claim whatsoever upon it until the father's death.  And it was stated: If the son sold the estate  during the lifetime of his father, and died while his father was still alive, R. Johanan said: The buyer does not acquire ownership;  and Resh Lakish said: The buyer does acquire ownership.  R. Johanan said that 'the buyer does not acquire ownership', because possession of usufruct is like possession of the capital;  and Resh Lakish said that 'the buyer does acquire ownership', because possession of usufruct is not like possession of the capital. BUT IF THE CHILD IS NOT VIABLE etc. A Tanna taught: It has been said in the name of R. Eliezer that  he must put her out by means of a letter of divorce. Said Raba: R. Meir and R. Eliezer taught the same law.  R. Eliezer, in the ruling just mentioned, R. Meir [in the following Baraitha] wherein it was taught: A man shall not marry the pregnant, or nursing wife of another;  and if he married, he must put her out and never remarry her; so R. Meir. But the Sages said: He shall let her go.  and at the proper time  he may marry her again. Abaye said to him:  How do you arrive at such a conclusion which may possibly be wrong?  R. Eliezer's ruling might extend to the present case  only because the levir is encroaching  upon the prohibition of 'brother's wife', which is Pentateuchal,  but there,  where the prohibition is only Rabbinical,  he may hold the same view as the Rabbis. Alternatively, it is possible that R. Meir's ruling extends only to that case because the prohibition is Rabbinical,  and the Sages have given more force to their provisions than to those which are Pentateuchal,  but not to the case here,  where the prohibition is Pentateuchal,  and people as a rule keep away from it. Raba said: Even according to the ruling of the Rabbis  he must let her go from him by means of a letter of divorce.  Said Mar Zutra: This may also be deduced, since the expression used was 'he shall put her out'  and not 'he shall let her part'.  This proves it. R. Ashi said to R. Hoshaia son of R. Idi: 'Elsewhere it was taught.  "R. Simeon b. Gamaliel said: Any human child  that survived for thirty days cannot be regarded as a miscarriage".  Had he not lived so long,  however, he would have been a doubtful case.  But it was also stated: Where he  died within thirty days  and she  was subsequently  betrothed,  Rabina said in the name of Raba that if she  was the wife of an Israelite  she must perform the halizah  and if she was the wife of a priest  she must not perform the halizah.  R. Mesharsheya  said in the name of Raba: The one as well as the other must perform the halizah. Said Rabina to R. Mesharsheya: