Reference for Yevamot 72:15

רב משרשיא משמיה דרבא אמר אחת זו ואחת זו חולצת

Had he not lived so long,<span class="x" onmousemove="('comment',' [Rashi: By dying a natural death; Tosaf. If he was killed; for if he died a natural death within thirty days even the Rabbis would regard him as a miscarriage, v. Tosaf, s.v. [H]. ');">⁴⁰</span> however, he would have been a doubtful case.<span class="x" onmousemove="('comment',' And his mother would have had to perform halizah only, but would not have been allowed to contract the levirate marriage. ');">⁴¹</span> But it was also stated: Where he<span class="x" onmousemove="('comment',' The child of a sister-in-law whose husband had died without having left any other issue. ');">⁴²</span>

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