TT #689 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:06
And it shall be that the firstborn that she bears shall succeed to the name of his dead brother, so that his name shall not be blotted out from Israel.
Torah Temimah points to Bekhorot / Rambam.
TT lemma: וְהָיָה הַבְּכוֹר.
כַּבְּכוֹר – מַה בְּכוֹרָה חוֹזֶרֶת בַּיּוֹבֵל אַף חֵלֶק יָבָם חוֹזֵר בַּיּוֹבֵל.
English: Like a firstborn — just as the firstborn’s double portion returns in the Jubilee, so the yavam’s share returns in the Jubilee.
On the daf / in context: The comparison extends to the Jubilee rules that apply to the firstborn’s extra portion.
Analogy extending Jubilee rules to the yavam’s share.
The portion acquired by the yavam through yibbum is subject to the same Jubilee return rules as the firstborn’s double portion.