Question? The Mishnah taught that (if it has in it a quarter Kav of another seed), he must reduce it. How must he reduce it? By reducing the quarter or by increasing the Seah? (The Gemara leaves this question unanswered.)

Question: Didn't R. Abahu teach from R. Yochanan - Any prohibition that was rendered Batel by inadvertently increasing the permitted one - it's permitted. If it was done intentionally, it's prohibited. But here he's doing it intentionally?

Answer: There, you are increasing the permitted one to negate the prohibited one. Here, you are reducing merely because of the Rabbinic prohibition of Maris HaAyin which they permitted actively reducing.

The Mishnah taught - R. Yosi said that he should remove all of the quarter Kav, (whether it contains one or two species). What's his reasoning for removing all of it? Once he begins to remove it, he should remove all of it.

R. Yosi agrees that if there was originally less than an a quarter, he does not need to fix it.

Question: If there was a quarter Kav comprising of two species - is he obligated to remove only one of those two species or both of them? (The Gemara leaves this question unanswered.)

Question: The Mishnah taught that R. Shimon says - The prohibition of a quarter Kav of another seed is only if it is entirely from one type of seed. How much of the mixture can consist of these multiple types of seeds (as long as no one type is a quarter Kav).

Answer: Until a quarter of the Seah.

Question: If he added more of the primary produce to the Seah, the mixture again becomes permitted.

Just as R. Shimon said that two species don't combine to prohibit, so too he says here that two species don't combine to permit...

How is that? If there were 221/2 quarters of wheat and a 1/2 quarter of barley (it is still permitted, since there isn't a quarter in 24 quarters; but on the other hand, they do not combine to be considered one species, so) if less than a quarter of lentils then fell in, since the barley doesn't combine with the wheat to permit, there isn't enough wheat to permit it because of the lentils that fell in.