Reference for Yevamot 63:7

<big><strong>גמ׳</strong></big> פשיטא השתא ומה התם דלא מידחיא מהאי ביתא לגמרי אמרת לא הכא דקא מידחיא מהאי ביתא לגמרי לא כ"ש תנא הא תנא ברישא והך חזיא להיתירא ושריא והדר חזיא לאיסורא ואיידי דחביבה ליה אקדמה ומשנה לא זזה ממקומה

it has been said, 'No',<span class="x" onmousemove="('comment',' I.e., she has been forbidden to the second brother, after the death of the third brother who had married her, owing to the original prohibition which may have lasted one moment only. even after his wife (her sister) had died. ');">²⁰</span> how much more so here<span class="x" onmousemove="('comment',' Our Mishnah where only two brothers are involved. ');">²¹</span> where the widow is completely excluded from that house!<span class="x" onmousemove="('comment',' When her husband died there was not a single brother whom she was permitted to marry. What need, then, was there for our Mishnah? ');">²²</span>

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