TT #668 · 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 / Rambam.
TT lemma: וּלְקָחָהּ.
וּלְקָחָהּ – לְזוֹ וְלֹא לְאַחֶרֶת; פְּרָט לָעֶרְוָה וּלְצָרָתָהּ.
English: “And he shall take her” — this one and not another; excluding an ervah and her co-wife.
On the daf / in context: Only a woman who is eligible for ordinary marriage can fall under the zikah of yibbum.
Mi’ut excluding forbidden relationships.
An ervah (and her co-wife) is exempt from both yibbum and chalitzah.