Reference for Bava Batra 254:13

רישא רבי יהודה וסיפא רבנן

In what legal respect?<span class="x" onmousemove="('comment',' Lit., 'to what law'; under what legal circumstances is it necessary, according to the Rabbis, for a father to declare which of his sons is his firstborn? ');">¹²</span>

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