Yevamot

R. Zebid, however, stated: No children are possible prior to the appearance of the marks of puberty.  Then let an examination be held!2   — There is the possibility that they might have fallen off.  This reply is perfectly satisfactory according to him who holds that such a possibility is taken into consideration;  what, however, can be said according to him who holds that no such contingency need be considered? — Even according to him who holds that no such contingency need be considered, the possibility must be taken into consideration in this case on account of the pains of birth.5 HOW IS THE EXEMPTION OF THEIR RIVALS [BY THE WOMEN MENTIONED] TO BE UNDERSTOOD? Etc. Whence is this law  deduced? — Rab Judah replied: [From] Scripture which stated, li-zeror,  [implying that] the Torah included many rivals.  R. Ashi replied. 'It  is arrived at by reasoning: Why is a rival forbidden? Surely because she takes the place of the forbidden relative; the rival's rival also takes the place of the forbidden relative'. HOW [IS ONE TO UNDERSTAND THE STATEMENT THAT] IF THEY HAD DIED etc. Even if he  married  first and then divorced?  This, then, would be contradictory [to the following Mishnah]: '[The case of] three brothers two of whom were married to two sisters and the third was married to a stranger, and one of the husbands of the sisters divorced his wife while the one who married the stranger died, and he who had divorced his wife then married the widow  and died, is one concerning which it has been said, that if they died or were divorced, their rivals are permitted'.  The reason, then,  is because the divorce  took place first and the marriage  was subsequent to it, but had the marriage  taken place first and the divorce  after it, [the rival would] not [have been permitted]!  — R. Jeremiah replied: Break it up:  He who taught the one did not teach the other. The one Tanna  is of the opinion that it is the death  which subjects the widow to the levirate marriage  while the other  holds the opinion that it is the original marriage that subjects her to the levirate marriage.  Raba said: [Both statements] may, in fact, represent the views of [one Tanna,] it  being a case of 'this; and there is no need to state that'. WHOSOEVER IS ENTITLED TO MAKE A DECLARATION OF REFUSAL [etc.]. Then let her  declare her refusal now  and thus enable [her rival] to be married to the levir!  May it then  be suggested that this supports R. Oshaiah? For R. Oshaiah said: She  may annul [the levir's] ma'amar  by her declaration of refusal,  but may not sever by such a declaration the levirate bond!  — No;  the case of the rival of a forbidden relative is different;  for Rami b. Ezekiel learnt: If a minor made a declaration of refusal against her husband she is permitted to marry his father.  If, however, she made her declaration of refusal against the levir  she is forbidden to marry his father.  From this it clearly follows that from the moment she becomes subject to the levirate marriage  she is looked upon as his  daughter-in-law; similarly here also  she is looked upon as the rival of his daughter from the moment she becomes subject to the levirate marriage. MISHNAH. [IN THE CASE OF THE FOLLOWING] SIX RELATIVES, MARRIAGE WITH WHOM IS MORE RESTRICTED THAN WITH THESE,  IN THAT THEY MAY ONLY BE MARRIED TO STRANGERS,  MARRIAGE WITH THEIR RIVALS IS PERMITTED:  HIS MOTHER.  HIS FATHER'S WIFE,  HIS FATHER'S SISTER,  HIS PATERNAL SISTER.  HIS FATHER'S BROTHER'S WIFE  AND HIS PATERNAL BROTHER'S WIFE. BETH SHAMMAI PERMIT THE RIVALS  TO THE SURVIVING BROTHERS, AND BETH HILLEL PROHIBIT THEM.