Yevamot

Those two which resemble one another  are reckoned as one, and thus [the total is] sixteen.' 'But, after all, I saw that these were written down as forbidden!'  The other said to him: 'Granted that this is so, would you have relied upon that list, if the cases had been written down as permitted? "Has Mar the son of Rabana signed them?" [you would have argued]. Now then that they have been written down as forbidden, [you might also argue]. "Mar the son of Rabana has not signed them". It was taught at the School of R. Hiyya: The third generation of his son,  of his daughter.  of the son of his wife  or of the daughter of his wife  [is forbidden as incest of the] second degree; the fourth generation  through his father-in-law  or his mother-in-law  [is forbidden as incest of the] second degree. Said Rabina to R. Ashi: Why is the wife included in the ascending line  and not included in the descending line?  -In the case of the ascending line, where the prohibition is due to his wife, she is included; in the descending line, where the prohibition is not due to his wife,  she is not included. But, surely, there is the case of the son of his wife and the daughter of his wife whose prohibition is due to his wife who is, nevertheless, not included! — As he enumerated three generations in the descending line on his side  and did not include her, he also enumerated three generations in the descending line on her side  and did not include her. Said R. Ashi to R. Kahana: Are the second degrees of incest of the School of R. Hiyya subject to the limitation  or not? Come and hear what Rab said: 'Four [categories of forbidden] women are subject to a limitation',  but no more. But is it not possible that Rab was only referring to that Baraitha! Come and hear: 'The third' and 'the fourth',  which implies the third and fourth generations only but no further. But is it not possible [that this meant] from the third generation onwards  and from the fourth generation onwards! Raba said to R. Nahman, 'Has the Master seen the young scholar who came from the West  and stated: The question was raised in the West whether the second degrees of incest were forbidden as a preventive measure among proselytes or not'? — The other replied: Seeing that even in respect of actual incest, but for the fear that they might be said to have exchanged a [religion of] stricter for [one of] more easy-going sanctity, the Rabbis would not have imposed upon them any preventive measures,  is there any question [that they should have done so in respect of] the second degrees? Said R. Nahman: As the subject of proselytes has come up,  let us say something about them: Maternal brothers may not tender evidence;  if, however, they did, their evidence is valid.  Paternal brothers may tender evidence without challenge. Amemar said: Even maternal brothers may tender evidence without challenge. And why is this case different from incest?  — Matters of incest lie in everybody's hands;  evidence is entrusted to Beth din, and [they know that] one who has become a proselyte is like a child newly born. MISHNAH. IF ONE HAS ANY KIND OF BROTHER,  [THAT BROTHER] IMPOSES UPON HIS BROTHER'S WIFE THE OBLIGATION OF THE LEVIRATE MARRIAGE AND IS DEEMED TO BE HIS BROTHER IN EVERY RESPECT. FROM THIS IS EXCLUDED A BROTHER BORN FROM A SLAVE OR A HEATHEN. IF ONE HAS ANY KIND OF SON, [THAT SON] EXEMPTS HIS FATHER'S WIFE FROM THE LEVIRATE MARRIAGE, IS LIABLE TO PUNISHMENT FOR STRIKING OR CURSING [HIS FATHER]. AND IS DEEMED TO BE HIS SON IN EVERY RESPECT. FROM THIS IS EXCLUDED THE SON OF A SLAVE OR A HEATHEN. GEMARA. What does the expression ANY KIND include? Rab Judah said: It includes a bastard. Is not this obvious? Surely, he is his brother! — It might have been assumed that 'brotherhood'  here should be deduced from 'brotherhood' in the case of the sons of Jacob;  as there they were all legitimate and untainted, so here also [the brothers must be] legitimate and untainted; hence we were taught [that it is not so]. [Might we still suggest that it is so?] — Since he  has at any rate the power to confer exemption from the levirate marriage