Reference for Bekhorot 91:11

איזהו בכור לנחלה ואינו בכור לכהן

OR ONE BORN IN THE NINTH MONTH WHOSE HEAD CAME FORTH DEAD,<span class="x" onmousemove="('comment',' And was then withdrawn, the companion coming out subsequently. The first offspring therefore exempts the latter from redemption, but since it is dead, the latter offspring is the first-born as regards inheritance.');">⁷</span>

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