TT #675 · 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 11a.
TT lemma: עָלֶיהָ.
עָלֶיהָ וְלֹא עַל צָרָתָהּ – הַבָּא עַל יְבִמְתּוֹ וּבָא אֶחָד מִן הָאַחִים עַל צָרָתָהּ עוֹבֵר בַּעֲשֵׂה.
English: “Upon her” and not upon her co-wife — one who has relations with his yevamah and then one of the brothers has relations with her co-wife violates a positive commandment.
On the daf / in context: The singular language creates an aseih (positive commandment) that excludes the co-wife.
Derash creating a positive commandment from the exclusive language.
After one brother has performed yibbum, relations by another brother with the co-wife violate the positive commandment “upon her (alone).”