(Exodus, Ibid. 9) "And if to his son he designate her (as a wife)": He designates her to his son, but not to his brother. For it would follow (that he does designate her to his brother), viz.: If he designates his son, who does not take his place through yibum (levirate marriage), how much more so, his brother, who does take his place through yibum! — No, this may be true of his son, who takes his place vis-à-vis (reversion to his father of) a (field of) holding (on the Yovel), (as opposed to his brother, who does not.) It is, therefore, written "And if to his son he designate her" — to his son and not to his brother.