Reference for Yevamot 36:6

ר"ש אומר מייבם לאיזו מהן שירצה או חולץ לאיזו מהן שירצה:

AND THE SECOND PERFORMED THE LEVIRATE MARRIAGE WITH HIS [DECEASED] BROTHER'S WIFE, AND AFTER A [THIRD] BROTHER WAS BORN THE SECOND DIED,<span class="x" onmousemove="('comment',' Without issue. ');">²³</span> THE FIRST<span class="x" onmousemove="('comment',' The widow of the first deceased brother who is now also the widow of the second. ');">²⁴</span> IS EXEMPT<span class="x" onmousemove="('comment',' From halizah and marriage with the third brother. ');">²⁵</span> ON ACCOUNT OF HER BEING THE WIFE OF HIS BROTHER WHO WAS NOT HIS CONTEMPORARY', WHILE THE SECOND IS EXEMPT AS HER RIVAL.<span class="x" onmousemove="('comment',' Both having been the wives of the second brother. ');">²⁶</span> IF HE<span class="x" onmousemove="('comment',' The second brother. ');">²⁷</span>

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