I am puzzled. It sais on Amud Beith that
"Amar Mar Amar Rebbi, Nireen Divrei Rabi Yossi Be muchlat Ve Divrei Rabbi Meyir Be Musgar". And then the Gmara sais that this is the oposite of what he said before.
However, if we look at the bottom of Amud Alef we see that it's not the oposite. That's exactly what Rebbi said on Amud Beith "Nireen divrei Rabi Meyir Bemusgar Vedivrei Rabi Yossi Bemuchlat". Isn't that what he said on Amud baith?
Why do the Gmara sais that it's the oposite?
When the Gemara says "Amar Mar..." ("the master said..."), it is quoting the Beraisa that it mentioned earlier on the botton of Amud Alef. It is not presenting a new Beraisa.
Then, when the Gemara asks, "v'ha'Tanya Ifcha" ("but there is a Beraisa that says the opposite!"), it is referring to another Beraisa which is not quoted by the Gemara in full. In that other Beraisa, Rebbi rules like Rebbi Yosi in the case of a Musgar, and like Rebbi Meir in the case of a Muchlat.
(Granted, it is a little confusing, because when the Gemara on the bottom of Amud Alef cites the Gemara, it mentions Rebbi Meir/Muchlat first, and then it mentions Rebbi Yosi/Musgar, and then when it re-quotes that same Beraisa here when it says "Amar Mar...," it mentions Rebbi Yosi/Musgar first, and then Rebbi Meir/Muchlat! Indeed, the DIKDUKEI SOFRIM (which fixes the text of our printing of the Gemara by comparing it with other earlier printings and manuscripts) corrects the order here, so that it reads exactly like it reads on Amud Alef.)