(Beraisa): Terumas Ma'aser of Demai [may be taken from Tahor on Tamei].

Question: See how [this is]?! Even Terumas Ma'aser of Vadai may be taken from Tahor on Tamei, and all the more so Terumas Ma'aser of Demai!

Answer (R. Yosi): We discuss Terumah Gedolah. It is a Safek whether he separated Terumah or did not separate (this is like Demai).

Question: Just like you say (Demai 5:11) that when one separates [Terumas Ma'aser] from Vadai on Demai, it is Terumah, and [the Kohen] may not eat it until separating on it Terumah and Ma'aseros (lest the Demai was fixed, and the 'Terumah' is really Tevel), you should say so [also] about Demai on Demai! (The Mishnah did not say so for Demai on Demai!)

Answer (R. Shimon bar Barsanah): This discusses when he wants to eat it (first he must separate Terumah and Ma'aseros), and this discusses when he wants to burn it (e.g. oil. Then, Chachamim were not stringent to be concerned lest it is Tevel. We explained this like HA'GAON RAV C. KANIEVSKY, SHLITA.)