Yevamot

and partially pulled down.  Well, let the assumption be made!  — Had he first contracted the levirate marriage and then participated in the halizah, no objection could be raised — 3 The preventive measure, however, has been enacted against the possibility of his participating in the halizah first and contracting the levirate marriage afterwards and thus placing himself under the prohibition of That doth not build up,  the All Merciful having said, 'Since he had not built  he must never again build'. Raba said: If he  gave a letter of divorce in respect of his ma'amar, her rival  is permitted;  but she herself is forbidden, because she might be mistaken for one who is the holder of a letter of divorce.  Others say that Raba said: If he  gave a letter of divorce in respect of his ma'amar even she herself becomes permitted.  What is the reason? — Because what he has done to her he has taken back. MISHNAH. IF TWO BROTHERS WERE MARRIED TO TWO SISTERS, AND ONE OF THE BROTHERS DIED, AND AFTERWARDS THE WIFE OF THE SECOND BROTHER DIED, BEHOLD, SHE  IS FORBIDDEN TO HIM  FOREVER, SINCE SHE WAS FORBIDDEN TO HIM FOR ONE MOMENT. GEMARA. Is not this obvious? If there,  where she  was not entirely excluded from that house  it has been said, 'No',  how much more so here  where the widow is completely excluded from that house!  -The Tanna had taught first this,  while the other  was regarded by him as a permissible case,  and so he permitted it — 25 Later, however, he came to regard it as a case that was to be forbidden;  and, as it was dear to him  he placed it first; while our Mishnah was allowed to remain in its original form. Our Rabbis learned: If he  had intercourse with her,  he is guilty on account of both 'his brother's wife'  and 'his wife's sister';  so R. Jose. R. Simeon said: He is guilty on account of 'his brother's wife' on]y. But, surely. it was taught that R. Simeon said: He is guilty on account of 'his wife's sister' only! — This is no difficulty: There, it is a case where the surviving brother had married first  and the deceased had married afterwards;  here it is a case where the deceased had married first and the surviving brother afterwards.  As to R. Simeon, in the case where the deceased had married first and the surviving brother married afterwards, let her, since the prohibition of wife's sister cannot take effect, be permitted even to contract the levirate marriage! — R. Ashi replied: The prohibition of wife's sister remains suspended, and as soon as the prohibition of brother's wife is removed  the prohibition of wife's sister comes into force; hence It cannot be treated as non-existent. Does, then, R. Jose hold the view that one prohibition may be imposed upon another? Surely, it was taught: A man who committed a transgression which involves two death penalties  is punished by the severer one. R. Jose said: He is to be dealt with In accordance with that prohibition which came into force first.  And it was taught: How is one to understand R. Jose's statement that sentence must be in accordance with the prohibition which came into force first? [If the woman was first] his mother-in-law  and then became also a married women, he is to be sentenced for [an offence against] his mother-in-law; if she was first a married woman and then became his mother-in-law, he is to be sentenced for [an offence against] a married woman!