Yevamot

the latter  gave her a letter of divorce he has not thereby disqualified her from marrying a priest',  it may be inferred that she requires no divorce;  for should she require a divorce, why does he not disqualify her from marrying a priest!  — Rather,  in the final clause it will be assumed  that the betrothal was an erroneous one.  In the first clause also [let it be said that] it would be assumed that the marriage was an erroneous one!  The Rabbis have penalized her.  Then let them penalize her in the final clause also! — In the first clause where she committed a forbidden act  they penalized her; in the final clause where she did not commit a forbidden act, the Rabbis did not penalize her. SHE HAS NO [CLAIM TO HER] KETHUBAH, [because] what is the reason why the Rabbis have provided a kethubah for a woman? In order that it may not be easy for the husband  to divorce her!  But in this case let it be easy for him, to divorce her. SHE HAS NO [CLAIM TO] … USUFRUCT, MAINTENANCE OR EVEN WORN CLOTHES, [because] the conditions  entered in the kethubah  are subject to the same laws as the kethubah  itself. IF SHE HAD TAKEN ANYTHING FROM THE ONE OR FROM THE OTHER, [SHE MUST RETURN IT]. Is this not obvious! — As it might haved been assumed that since she has already seized it, it is not to be taken from her, hence we were taught [that SHE MUST RETURN IT]. THE CHILD … IS A BASTARD. Elsewhere we learned: Terumah  from levitically unclean produce may not be set apart for that which is levitically clean.  If, however, such terumah has been set apart it is valid if the act was done in error, but if it was done wilfully it is null and void.  Now what is meant by 'it is null and void'? — R. Hisda replied: The act is absolutely null and void, even that griva  [which has been designated as terumah] returns to its former state of tebel.  R. Nathan son of R. Oshaia replied: It is null and void in respect of making the remainder  fit for use, but [that which has been set apart] becomes terumah.  R. Hisda does not give the same explanation as R. Nathan son of R. Oshaia, for, should it be said [that the portion set apart] is lawful terumah, it might sometimes happen that one would wilfully neglect to set apart the terumah [from the remainder]. But why should this be different from, [the following case concerning] which we learned: If a man has set apart as terumah a cucumber which was found to be bitter, or a melon which turned out to be decayed  [the fruit becomes] terumah; but [from the remainder] terumah must again be set apart!  Do you raise an objection from a case where one has acted unwittingly  against a case where one has acted wilfully?  Where one has acted unwittingly,  no forbidden act has been committed; when, however, one has acted wilfully,  a forbidden act has been committed. A contradiction, however, was pointed out between two acts committed unwittingly: Here  it is stated, 'It is lawful terumah if the act was done unwittingly',  while there sit was stated, 'Terumah,' but [from the remainder] terumah must again be set apart'! — There,  it is an erroneous act amounting almost  to a wilful one, since he should have tasted it. A contradiction was also pointed out between two cases of wilful action: Here  it is stated, 'but if it was done wilfully, it is null and void', while elsewhere we learned: If a man has set apart as terumah [the produce] of an unperforated plant-pot  for [the produce of] a perforated pot,  [the former becomes] terumah but [from the latter] terumah must again be separated!  — In [the case of produce grown in] two different vessels  a man would obey;  in [that of] one vessel  he would not obey. Now according to R. Nathan, son of R. Oshaia, who explained that 'the act is null and void in respect of making the remainder fit for use but [that that which has been set apart] becomes terumah.