For the source text click/tap here: Chullin 132
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The Mishnah states that when a Bechor becomes mixed with a herd of cows and all of them are slaughtered by a single Shochet, Zero'a, Lechayayim, and Keivah must be given from all the cows except for one. RASHI (DH v'Im Echad) explains that Matnos Kehunah are not given from a Bechor, because "Ein Kedushah Chal Al Kedushah" -- one form of Kedushah (Kedushas Matnos Kehunah) cannot take effect on an object that already has Kedushah (Kedushas Bechor).
Ulla used to give kohen's gifts to a kohenet - a daughter of a kohen. Why? When the Torah told to give the gifts to a kohen, we understand that a kohenet is excluded.
However, when it said the word "kohen" again, this is a double exclusion, which always means an inclusion, and a kohenet is now included. Rav Pappa was married to a kohenet, and people would bring him kohen's gifts.
We explore the levitical status and gifts thereof,,,,