TT #658 · 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 54b.
TT lemma: יְבָמָהּ יָבֹא עָלֶיהָ.
וַאֲפִלּוּ בְּהַעֲרָאָה קוֹנָה, דְּיָלְפִינַן בִּיאָה בִּיאָה.
English: Even initial contact (ha’ara’ah) acquires her, for we learn “bi’ah” from “bi’ah” elsewhere.
On the daf / in context: The gezerah shavah with other contexts of bi’ah teaches that full consummation is not required; the beginning of the act suffices.
Gezerah shavah on “bi’ah.”
The initial stage of intercourse is sufficient to effect yibbum.