TT #664 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:05
When brothers dwell together and one of them dies and has no son, the wife of the dead shall not be outside to a strange man; her husband’s brother shall come upon her and take her to himself as a wife and perform the duty of a husband’s brother for her.
Torah Temimah points to Yevamot 39a / Kiddushin.
TT lemma: וּלְקָחָהּ לוֹ לְאִשָּׁה.
יְבָמָהּ יָבֹא עָלֶיהָ – זוֹ בִּיאָה; וּלְקָחָהּ לוֹ לְאִשָּׁה – זֶה הַמַּאֲמָר.
English: “Her yavam shall come upon her” — this is the act of intercourse; “and he shall take her to himself as a wife” — this is the ma’amar (preliminary kiddushin).
On the daf / in context: The verse is read as distinguishing the final act of bi’ah from the preparatory verbal/monetary ma’amar.
Derash partitioning the verse into ma’amar and bi’ah.
Ma’amar (a form of kiddushin) may precede the bi’ah of yibbum, but only bi’ah completes the acquisition.