Halakhah for Yevamot 34:11
אי הוה אמר הכי ה"א הנ"מ בתרי אבל בחד יש זיקה
is derived from the father and not from the mother!<span class="x" onmousemove="('comment',' What need then was there for the expression 'brethren'? ');"><sup>32</sup></span> -It<span class="x" onmousemove="('comment',' The expression 'brethren'. ');"><sup>33</sup></span> was necessary. For it might have been assumed that whereas this<span class="x" onmousemove="('comment',' Levirate marriage. ');"><sup>34</sup></span> is an anomaly,<span class="x" onmousemove="('comment',' Lit., 'something novel'. ');"><sup>35</sup></span>
Sefer HaChinukh
From the laws of the commandment is that which they, may their memory blessed, said (Yevamot 17b), "'When brothers dwell together' - to exclude the wife of a brother who was not in his world"; meaning that [then] she does not have an obligation of levirate marriage and not of release - for example, [if] this brother was born after his brother [that was married and had no children] died. And that which they also inferred (Yevamot 17b), "'Brothers together' - that are together in inheritance, to exclude brothers [born only] from the mother," who are not obligated in levirate marriage and release. "'And has no (ein) son' - look into (ayen) him" (Yevamot 22b). [This is] meaning to say that if the brother did have a son or daughter from any place, or the son of a son or the son of a daughter or the daughter of a daughter or any one that came out from his 'thigh' - there is no commandment of levirate marriage or release there, for the reason that we mentioned concerning the commandment of levirate marriage.
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