Responsa for Yevamot 214:6

רב אסי אמר מיאנה בזה מותרת אפילו לו לימא כרבי אושעיא סבירא ליה דאמר אינה ממאנת לזיקתו בחד יבם הכי נמי דמציא עקרא הכא בשני יבמין עסקינן דאין מיאון לחצי זיקה

As<span class="x" onmousemove="('comment',' Lit., 'not?' ');">¹⁹</span> the recipient of a letter of divorce is forbidden to all [the brothers] as soon as she is forbidden to one<span class="x" onmousemove="('comment',' The levir who gave her the letter of divorce. ');">²⁰</span> so is there no difference here also.<span class="x" onmousemove="('comment',' The mi'un which causes her to be forbidden to marry one of the brothers causes her, as in the case of divorce, to be equally forbidden to all the other brothers. ');">²¹</span> Samuel, however, stated: If she<span class="x" onmousemove="('comment',' A minor. ');">¹⁶</span>

Teshuvot Maharam