Reference for Yevamot 63:3

אלא גזירה דילמא חליץ ברישא והדר מייבם וקם ליה באשר לא יבנה ורחמנא אמר כיון שלא בנה שוב לא יבנה

gave a letter of divorce in respect of his ma'amar, her rival<span class="x" onmousemove="('comment',' I.e., his first wife. ');">⁸</span> is permitted;<span class="x" onmousemove="('comment',' To the third surviving brother if the second also died without issue. The two widows are no longer rivals since the divorce has annulled the ma'amar, and they. being the widows of two different brothers, are now coming from two different houses. ');">⁹</span> but she herself is forbidden, because she might be mistaken for one who is the holder of a letter of divorce.<span class="x" onmousemove="('comment',' That was given to her in respect of the levirate bond as well as of the ma'amar, v. infra 52b. Such a sister-in-law is forbidden under the prohibition of That doth not build up (v. supra and notes 3, 4 and 5)' since in her case the levirate bond also had been severed. ');">¹⁰</span>

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